diff --git a/.env.example b/.env.example
index d5d35ed..c9cc51e 100644
--- a/.env.example
+++ b/.env.example
@@ -30,3 +30,10 @@ ASSOCIATION_NAME="Sportsclub XYZ"
 # OIDC_GROUPS_CLAIM defaults to "groups" (JWT claim name for group list).
 # OIDC_ADMIN_GROUP_NAME=admin
 # OIDC_GROUPS_CLAIM=groups
+
+# Optional: Vereinfacht accounting integration (finance-contacts sync)
+# If set, these override values from Settings UI; those fields become read-only.
+# VEREINFACHT_API_URL=https://api.verein.visuel.dev/api/v1
+# VEREINFACHT_API_KEY=your-api-key
+# VEREINFACHT_CLUB_ID=2
+# VEREINFACHT_APP_URL=https://app.verein.visuel.dev
diff --git a/assets/css/app.css b/assets/css/app.css
index 0219e1e..0149c5d 100644
--- a/assets/css/app.css
+++ b/assets/css/app.css
@@ -99,6 +99,25 @@
 /* Make LiveView wrapper divs transparent for layout */
 [data-phx-session] { display: contents }
 
+/* WCAG 1.4.12 Text Spacing: allow user stylesheets to adjust text spacing in popovers.
+   Popover content (e.g. from DaisyUI dropdown) must not rely on non-overridable inline
+   spacing; use inherited values so custom stylesheets can override. */
+[popover] {
+  line-height: inherit;
+  letter-spacing: inherit;
+  word-spacing: inherit;
+}
+
+/* WCAG 2 AA: success/error text on light backgrounds (e.g. base-200). Use instead of
+   text-success/text-error when contrast ratio of theme colors is insufficient. */
+.text-success-aa {
+  color: oklch(0.35 0.12 165);
+}
+
+.text-error-aa {
+  color: oklch(0.45 0.2 25);
+}
+
 /* ============================================
    Sidebar Base Styles
    ============================================ */
diff --git a/lib/accounts/user.ex b/lib/accounts/user.ex
index 92b9ef2..9ac7605 100644
--- a/lib/accounts/user.ex
+++ b/lib/accounts/user.ex
@@ -118,6 +118,8 @@ defmodule Mv.Accounts.User do
       change Mv.EmailSync.Changes.SyncUserEmailToMember do
         where [changing(:email)]
       end
+
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
     end
 
     create :create_user do
@@ -145,6 +147,8 @@ defmodule Mv.Accounts.User do
 
       # Sync user email to member when linking (User → Member)
       change Mv.EmailSync.Changes.SyncUserEmailToMember
+
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
     end
 
     update :update_user do
@@ -178,6 +182,8 @@ defmodule Mv.Accounts.User do
       change Mv.EmailSync.Changes.SyncUserEmailToMember do
         where any([changing(:email), changing(:member)])
       end
+
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
     end
 
     # Internal update used only by SystemActor/bootstrap and tests to assign role to system user.
@@ -211,6 +217,8 @@ defmodule Mv.Accounts.User do
       change Mv.EmailSync.Changes.SyncUserEmailToMember do
         where [changing(:email)]
       end
+
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
     end
 
     # Action to link an OIDC account to an existing password-only user
@@ -248,6 +256,8 @@ defmodule Mv.Accounts.User do
       change Mv.EmailSync.Changes.SyncUserEmailToMember do
         where [changing(:email)]
       end
+
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
     end
 
     read :get_by_subject do
@@ -328,6 +338,8 @@ defmodule Mv.Accounts.User do
       # Sync user email to member when linking (User → Member)
       change Mv.EmailSync.Changes.SyncUserEmailToMember
 
+      change Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange
+
       # Sync role from OIDC groups (e.g. admin group → Admin role) after user is created/updated
       change fn changeset, _ctx ->
         user_info = Ash.Changeset.get_argument(changeset, :user_info)
diff --git a/lib/membership/member.ex b/lib/membership/member.ex
index 476501c..7b70e89 100644
--- a/lib/membership/member.ex
+++ b/lib/membership/member.ex
@@ -117,6 +117,9 @@ defmodule Mv.Membership.Member do
       # Requires both join_date and membership_fee_type_id to be present
       change Mv.MembershipFees.Changes.SetMembershipFeeStartDate
 
+      # Sync member to Vereinfacht as finance contact (if configured)
+      change Mv.Vereinfacht.Changes.SyncContact
+
       # Trigger cycle generation after member creation
       # Only runs if membership_fee_type_id is set
       # Note: Cycle generation runs asynchronously to not block the action,
@@ -190,6 +193,9 @@ defmodule Mv.Membership.Member do
         where [changing(:membership_fee_type_id)]
       end
 
+      # Sync member to Vereinfacht as finance contact (if configured)
+      change Mv.Vereinfacht.Changes.SyncContact
+
       # Trigger cycle regeneration when membership_fee_type_id changes
       # This deletes future unpaid cycles and regenerates them with the new type/amount
       # Note: Cycle regeneration runs synchronously in the same transaction to ensure atomicity
@@ -243,6 +249,13 @@ defmodule Mv.Membership.Member do
              end)
     end
 
+    # Internal: set vereinfacht_contact_id after syncing with Vereinfacht API.
+    # Not exposed via code interface; used only by Mv.Vereinfacht.Changes.SyncContact.
+    update :set_vereinfacht_contact_id do
+      require_atomic? false
+      accept [:vereinfacht_contact_id]
+    end
+
     # Action to handle fuzzy search on specific fields
     read :search do
       argument :query, :string, allow_nil?: true
@@ -320,6 +333,12 @@ defmodule Mv.Membership.Member do
       authorize_if Mv.Authorization.Checks.HasPermission
     end
 
+    # Internal sync action: only SystemActor may set vereinfacht_contact_id (used by SyncContact change).
+    policy action(:set_vereinfacht_contact_id) do
+      description "Only system actor may set Vereinfacht contact ID"
+      authorize_if Mv.Authorization.Checks.ActorIsSystemUser
+    end
+
     # CREATE/UPDATE: Forbid member–user link unless admin, then check permissions
     # ForbidMemberUserLinkUnlessAdmin: only admins may pass :user (link or unlink via nil/empty).
     # HasPermission: :own_data → update linked; :read_only → no update; :normal_user/admin → update all.
@@ -593,6 +612,14 @@ defmodule Mv.Membership.Member do
       public? true
       description "Date from which membership fees should be calculated"
     end
+
+    # Vereinfacht accounting software integration: ID of the finance contact synced via API.
+    # Set by Mv.Vereinfacht.Changes.SyncContact; not accepted in create/update actions.
+    attribute :vereinfacht_contact_id, :string do
+      allow_nil? true
+      public? true
+      description "ID of the finance contact in Vereinfacht (set by sync)"
+    end
   end
 
   relationships do
@@ -1273,17 +1300,24 @@ defmodule Mv.Membership.Member do
     end
   end
 
-  # Extracts custom field values from existing member data (update scenario)
+  # Extracts custom field values from existing member data (update scenario).
+  # Actor must come from context; no system-actor fallback (per guidelines).
+  # When no actor is present we skip the load and return empty map.
   defp extract_existing_values(member_data, changeset) do
-    actor = Map.get(changeset.context, :actor)
-    opts = Helpers.ash_actor_opts(actor)
-
-    case Ash.load(member_data, :custom_field_values, opts) do
-      {:ok, %{custom_field_values: existing_values}} ->
-        Enum.reduce(existing_values, %{}, &extract_value_from_cfv/2)
-
-      _ ->
+    case Map.get(changeset.context, :actor) do
+      nil ->
         %{}
+
+      actor ->
+        opts = Helpers.ash_actor_opts(actor)
+
+        case Ash.load(member_data, :custom_field_values, opts) do
+          {:ok, %{custom_field_values: existing_values}} ->
+            Enum.reduce(existing_values, %{}, &extract_value_from_cfv/2)
+
+          _ ->
+            %{}
+        end
     end
   end
 
diff --git a/lib/membership/setting.ex b/lib/membership/setting.ex
index bb7d122..f56daa0 100644
--- a/lib/membership/setting.ex
+++ b/lib/membership/setting.ex
@@ -69,7 +69,11 @@ defmodule Mv.Membership.Setting do
         :club_name,
         :member_field_visibility,
         :include_joining_cycle,
-        :default_membership_fee_type_id
+        :default_membership_fee_type_id,
+        :vereinfacht_api_url,
+        :vereinfacht_api_key,
+        :vereinfacht_club_id,
+        :vereinfacht_app_url
       ]
     end
 
@@ -81,7 +85,11 @@ defmodule Mv.Membership.Setting do
         :club_name,
         :member_field_visibility,
         :include_joining_cycle,
-        :default_membership_fee_type_id
+        :default_membership_fee_type_id,
+        :vereinfacht_api_url,
+        :vereinfacht_api_key,
+        :vereinfacht_club_id,
+        :vereinfacht_app_url
       ]
     end
 
@@ -225,6 +233,33 @@ defmodule Mv.Membership.Setting do
       description "Default membership fee type ID for new members"
     end
 
+    # Vereinfacht accounting software integration (can be overridden by ENV)
+    attribute :vereinfacht_api_url, :string do
+      allow_nil? true
+      public? true
+      description "Vereinfacht API base URL (e.g. https://api.verein.visuel.dev/api/v1)"
+    end
+
+    attribute :vereinfacht_api_key, :string do
+      allow_nil? true
+      public? false
+      description "Vereinfacht API key (Bearer token)"
+      sensitive? true
+    end
+
+    attribute :vereinfacht_club_id, :string do
+      allow_nil? true
+      public? true
+      description "Vereinfacht club ID for multi-tenancy"
+    end
+
+    attribute :vereinfacht_app_url, :string do
+      allow_nil? true
+      public? true
+
+      description "Vereinfacht app base URL for contact view links (e.g. https://app.verein.visuel.dev)"
+    end
+
     timestamps()
   end
 
diff --git a/lib/mv/application.ex b/lib/mv/application.ex
index ea0c78e..1967ddd 100644
--- a/lib/mv/application.ex
+++ b/lib/mv/application.ex
@@ -7,6 +7,8 @@ defmodule Mv.Application do
 
   @impl true
   def start(_type, _args) do
+    Mv.Vereinfacht.SyncFlash.create_table!()
+
     children = [
       MvWeb.Telemetry,
       Mv.Repo,
diff --git a/lib/mv/authorization/checks/actor_is_system_user.ex b/lib/mv/authorization/checks/actor_is_system_user.ex
new file mode 100644
index 0000000..a614a83
--- /dev/null
+++ b/lib/mv/authorization/checks/actor_is_system_user.ex
@@ -0,0 +1,15 @@
+defmodule Mv.Authorization.Checks.ActorIsSystemUser do
+  @moduledoc """
+  Policy check: true only when the actor is the system user (e.g. system@mila.local).
+
+  Used to restrict internal actions (e.g. Member.set_vereinfacht_contact_id) so that
+  only code paths using SystemActor can perform them, not regular admins.
+  """
+  use Ash.Policy.SimpleCheck
+
+  @impl true
+  def describe(_opts), do: "actor is the system user"
+
+  @impl true
+  def match?(actor, _context, _opts), do: Mv.Helpers.SystemActor.system_user?(actor)
+end
diff --git a/lib/mv/config.ex b/lib/mv/config.ex
index bcbc8d9..d2ad66c 100644
--- a/lib/mv/config.ex
+++ b/lib/mv/config.ex
@@ -142,4 +142,160 @@ defmodule Mv.Config do
     |> Keyword.get(key, default)
     |> parse_and_validate_integer(default)
   end
+
+  # ---------------------------------------------------------------------------
+  # Vereinfacht accounting software integration
+  # ENV variables take priority; fallback to Settings from database.
+  # ---------------------------------------------------------------------------
+
+  @doc """
+  Returns the Vereinfacht API base URL.
+
+  Reads from `VEREINFACHT_API_URL` env first, then from Settings.
+  """
+  @spec vereinfacht_api_url() :: String.t() | nil
+  def vereinfacht_api_url do
+    env_or_setting("VEREINFACHT_API_URL", :vereinfacht_api_url)
+  end
+
+  @doc """
+  Returns the Vereinfacht API key (Bearer token).
+
+  Reads from `VEREINFACHT_API_KEY` env first, then from Settings.
+  """
+  @spec vereinfacht_api_key() :: String.t() | nil
+  def vereinfacht_api_key do
+    env_or_setting("VEREINFACHT_API_KEY", :vereinfacht_api_key)
+  end
+
+  @doc """
+  Returns the Vereinfacht club ID for multi-tenancy.
+
+  Reads from `VEREINFACHT_CLUB_ID` env first, then from Settings.
+  """
+  @spec vereinfacht_club_id() :: String.t() | nil
+  def vereinfacht_club_id do
+    env_or_setting("VEREINFACHT_CLUB_ID", :vereinfacht_club_id)
+  end
+
+  @doc """
+  Returns the Vereinfacht app base URL for contact view links (frontend, not API).
+
+  Reads from `VEREINFACHT_APP_URL` env first, then from Settings.
+  Used to build links like https://app.verein.visuel.dev/en/admin/finances/contacts/{id}.
+  If not set, derived from API URL by replacing host \"api.\" with \"app.\" when possible.
+  """
+  @spec vereinfacht_app_url() :: String.t() | nil
+  def vereinfacht_app_url do
+    env_or_setting("VEREINFACHT_APP_URL", :vereinfacht_app_url) ||
+      derive_app_url_from_api_url(vereinfacht_api_url())
+  end
+
+  defp derive_app_url_from_api_url(nil), do: nil
+
+  defp derive_app_url_from_api_url(api_url) when is_binary(api_url) do
+    api_url = String.trim(api_url)
+    uri = URI.parse(api_url)
+    host = uri.host || ""
+
+    if String.starts_with?(host, "api.") do
+      app_host = "app." <> String.slice(host, 4..-1//1)
+      scheme = uri.scheme || "https"
+      "#{scheme}://#{app_host}"
+    else
+      nil
+    end
+  end
+
+  defp derive_app_url_from_api_url(_), do: nil
+
+  @doc """
+  Returns true if Vereinfacht is fully configured (URL, API key, and club ID all set).
+  """
+  @spec vereinfacht_configured?() :: boolean()
+  def vereinfacht_configured? do
+    present?(vereinfacht_api_url()) and present?(vereinfacht_api_key()) and
+      present?(vereinfacht_club_id())
+  end
+
+  @doc """
+  Returns true if any Vereinfacht ENV variable is set (used to show hint in Settings UI).
+  """
+  @spec vereinfacht_env_configured?() :: boolean()
+  def vereinfacht_env_configured? do
+    vereinfacht_api_url_env_set?() or vereinfacht_api_key_env_set?() or
+      vereinfacht_club_id_env_set?()
+  end
+
+  @doc """
+  Returns true if VEREINFACHT_API_URL is set (field is read-only in Settings).
+  """
+  def vereinfacht_api_url_env_set?, do: env_set?("VEREINFACHT_API_URL")
+
+  @doc """
+  Returns true if VEREINFACHT_API_KEY is set (field is read-only in Settings).
+  """
+  def vereinfacht_api_key_env_set?, do: env_set?("VEREINFACHT_API_KEY")
+
+  @doc """
+  Returns true if VEREINFACHT_CLUB_ID is set (field is read-only in Settings).
+  """
+  def vereinfacht_club_id_env_set?, do: env_set?("VEREINFACHT_CLUB_ID")
+
+  @doc """
+  Returns true if VEREINFACHT_APP_URL is set (field is read-only in Settings).
+  """
+  def vereinfacht_app_url_env_set?, do: env_set?("VEREINFACHT_APP_URL")
+
+  defp env_set?(key) do
+    case System.get_env(key) do
+      nil -> false
+      v when is_binary(v) -> String.trim(v) != ""
+      _ -> false
+    end
+  end
+
+  defp env_or_setting(env_key, setting_key) do
+    case System.get_env(env_key) do
+      nil -> get_vereinfacht_from_settings(setting_key)
+      value -> trim_nil(value)
+    end
+  end
+
+  defp get_vereinfacht_from_settings(key) do
+    case Mv.Membership.get_settings() do
+      {:ok, settings} -> settings |> Map.get(key) |> trim_nil()
+      {:error, _} -> nil
+    end
+  end
+
+  defp trim_nil(nil), do: nil
+
+  defp trim_nil(s) when is_binary(s) do
+    t = String.trim(s)
+    if t == "", do: nil, else: t
+  end
+
+  @doc """
+  Returns the URL to view a finance contact in the Vereinfacht app (frontend).
+
+  Uses the configured app base URL (or derived from API URL) and appends
+  /en/admin/finances/contacts/{id}. Returns nil if no app URL can be determined.
+  """
+  @spec vereinfacht_contact_view_url(String.t()) :: String.t() | nil
+  def vereinfacht_contact_view_url(contact_id) when is_binary(contact_id) do
+    base = vereinfacht_app_url()
+
+    if present?(base) do
+      base
+      |> String.trim_trailing("/")
+      |> then(&"#{&1}/en/admin/finances/contacts/#{contact_id}")
+    else
+      nil
+    end
+  end
+
+  defp present?(nil), do: false
+  defp present?(s) when is_binary(s), do: String.trim(s) != ""
+  defp present?(_), do: false
 end
diff --git a/lib/mv/vereinfacht/changes/sync_contact.ex b/lib/mv/vereinfacht/changes/sync_contact.ex
new file mode 100644
index 0000000..99875e0
--- /dev/null
+++ b/lib/mv/vereinfacht/changes/sync_contact.ex
@@ -0,0 +1,91 @@
+defmodule Mv.Vereinfacht.Changes.SyncContact do
+  @moduledoc """
+  Syncs a member to Vereinfacht as a finance contact after create/update.
+
+  - If the member has no `vereinfacht_contact_id`, creates a contact via API and saves the ID.
+  - If the member already has an ID, updates the contact via API.
+  Runs in `after_transaction` so the member is persisted first. API failures are logged
+  but do not block the member operation. Requires Vereinfacht to be configured
+  (Mv.Config.vereinfacht_configured?/0).
+
+  Only runs when relevant data changed: on create always; on update only when
+  first_name, last_name, email, street, house_number, postal_code, or city changed,
+  or when the member has no vereinfacht_contact_id yet (to avoid unnecessary API calls).
+  """
+  use Ash.Resource.Change
+
+  require Logger
+
+  @synced_attributes [
+    :first_name,
+    :last_name,
+    :email,
+    :street,
+    :house_number,
+    :postal_code,
+    :city
+  ]
+
+  @impl true
+  def change(changeset, _opts, _context) do
+    if Mv.Config.vereinfacht_configured?() and sync_relevant?(changeset) do
+      Ash.Changeset.after_transaction(changeset, &sync_after_transaction/2)
+    else
+      changeset
+    end
+  end
+
+  defp sync_relevant?(changeset) do
+    case changeset.action_type do
+      :create -> true
+      :update -> relevant_update?(changeset)
+      _ -> false
+    end
+  end
+
+  defp relevant_update?(changeset) do
+    any_synced_attr_changed? =
+      Enum.any?(@synced_attributes, &Ash.Changeset.changing_attribute?(changeset, &1))
+
+    record = changeset.data
+    no_contact_id_yet? = record && blank_contact_id?(record.vereinfacht_contact_id)
+
+    any_synced_attr_changed? or no_contact_id_yet?
+  end
+
+  defp blank_contact_id?(nil), do: true
+  defp blank_contact_id?(""), do: true
+  defp blank_contact_id?(s) when is_binary(s), do: String.trim(s) == ""
+  defp blank_contact_id?(_), do: false
+
+  # Ash calls after_transaction with (changeset, result) only - 2 args.
+  defp sync_after_transaction(_changeset, {:ok, member}) do
+    case Mv.Vereinfacht.sync_member(member) do
+      :ok ->
+        Mv.Vereinfacht.SyncFlash.store(to_string(member.id), :ok, "Synced to Vereinfacht.")
+        {:ok, member}
+
+      {:ok, member_updated} ->
+        Mv.Vereinfacht.SyncFlash.store(
+          to_string(member_updated.id),
+          :ok,
+          "Synced to Vereinfacht."
+        )
+
+        {:ok, member_updated}
+
+      {:error, reason} ->
+        Logger.warning("Vereinfacht sync failed for member #{member.id}: #{inspect(reason)}")
+
+        Mv.Vereinfacht.SyncFlash.store(
+          to_string(member.id),
+          :warning,
+          Mv.Vereinfacht.format_error(reason)
+        )
+
+        {:ok, member}
+    end
+  end
+
+  defp sync_after_transaction(_changeset, error), do: error
+end
diff --git a/lib/mv/vereinfacht/changes/sync_linked_member_after_user_change.ex b/lib/mv/vereinfacht/changes/sync_linked_member_after_user_change.ex
new file mode 100644
index 0000000..cffb079
--- /dev/null
+++ b/lib/mv/vereinfacht/changes/sync_linked_member_after_user_change.ex
@@ -0,0 +1,71 @@
+defmodule Mv.Vereinfacht.Changes.SyncLinkedMemberAfterUserChange do
+  @moduledoc """
+  Syncs the linked Member to Vereinfacht after a User action that may have updated
+  the member's email via Ecto (e.g. User email change → SyncUserEmailToMember).
+
+  Attach to any User action that uses SyncUserEmailToMember. After the transaction
+  commits, if the user has a linked member and Vereinfacht is configured, syncs
+  that member to the API. Failures are logged but do not affect the User result.
+  """
+  use Ash.Resource.Change
+
+  require Logger
+  alias Mv.Membership.Member
+  alias Mv.Membership
+  alias Mv.Helpers.SystemActor
+  alias Mv.Helpers
+
+  @impl true
+  def change(changeset, _opts, _context) do
+    if Mv.Config.vereinfacht_configured?() and relevant_change?(changeset) do
+      Ash.Changeset.after_transaction(changeset, &sync_linked_member_after_transaction/2)
+    else
+      changeset
+    end
+  end
+
+  # Only sync when something that affects the linked member's data actually changed
+  # (email sync or member link), to avoid unnecessary API calls on every user update.
+  defp relevant_change?(changeset) do
+    Ash.Changeset.changing_attribute?(changeset, :email) or
+      Ash.Changeset.changing_relationship?(changeset, :member)
+  end
+
+  defp sync_linked_member_after_transaction(_changeset, {:ok, user}) do
+    case load_linked_member(user) do
+      nil ->
+        {:ok, user}
+
+      member ->
+        case Mv.Vereinfacht.sync_member(member) do
+          :ok ->
+            {:ok, user}
+
+          {:ok, _} ->
+            {:ok, user}
+
+          {:error, reason} ->
+            Logger.warning(
+              "Vereinfacht sync failed for member #{member.id} (linked to user #{user.id}): #{inspect(reason)}"
+            )
+
+            {:ok, user}
+        end
+    end
+  end
+
+  defp sync_linked_member_after_transaction(_changeset, result), do: result
+
+  defp load_linked_member(%{member_id: nil}), do: nil
+  defp load_linked_member(%{member_id: ""}), do: nil
+
+  defp load_linked_member(user) do
+    actor = SystemActor.get_system_actor()
+    opts = Helpers.ash_actor_opts(actor)
+
+    case Ash.get(Member, user.member_id, [domain: Membership] ++ opts) do
+      {:ok, %Member{} = member} -> member
+      _ -> nil
+    end
+  end
+end
diff --git a/lib/mv/vereinfacht/client.ex b/lib/mv/vereinfacht/client.ex
new file mode 100644
index 0000000..58e06a9
--- /dev/null
+++ b/lib/mv/vereinfacht/client.ex
@@ -0,0 +1,364 @@
+defmodule Mv.Vereinfacht.Client do
+  @moduledoc """
+  HTTP client for the Vereinfacht accounting software JSON:API.
+
+  Creates and updates finance contacts. Uses Bearer token authentication and
+  requires club ID for multi-tenancy. Configuration via ENV or Settings
+  (see Mv.Config).
+  """
+  require Logger
+
+  @content_type "application/vnd.api+json"
+
+  @doc """
+  Creates a finance contact in Vereinfacht for the given member.
+
+  Returns the contact ID on success. Does not update the member record;
+  the caller (e.g. SyncContact change) must persist `vereinfacht_contact_id`.
+
+  ## Options
+  - None; URL, API key, and club ID are read from Mv.Config.
+
+  ## Examples
+
+      iex> create_contact(member)
+      {:ok, "242"}
+
+      iex> create_contact(member)
+      {:error, {:http, 401, "Unauthenticated."}}
+  """
+  @spec create_contact(struct()) :: {:ok, String.t()} | {:error, term()}
+  def create_contact(member) do
+    base_url = base_url()
+    api_key = api_key()
+    club_id = club_id()
+
+    if is_nil(base_url) or is_nil(api_key) or is_nil(club_id) do
+      {:error, :not_configured}
+    else
+      body = build_create_body(member, club_id)
+      url = base_url |> String.trim_trailing("/") |> then(&"#{&1}/finance-contacts")
+      post_and_parse_contact(url, body, api_key)
+    end
+  end
+
+  @sync_timeout_ms 5_000
+
+  # In test, skip retries so sync fails fast when no API is running (avoids log spam and long waits).
+  defp req_http_options do
+    opts = [receive_timeout: @sync_timeout_ms]
+    if Mix.env() == :test, do: [retry: false] ++ opts, else: opts
+  end
+
+  defp post_and_parse_contact(url, body, api_key) do
+    encoded_body = Jason.encode!(body)
+
+    case Req.post(url, [body: encoded_body, headers: headers(api_key)] ++ req_http_options()) do
+      {:ok, %{status: 201, body: resp_body}} ->
+        case get_contact_id_from_response(resp_body) do
+          nil -> {:error, {:invalid_response, resp_body}}
+          id -> {:ok, id}
+        end
+
+      {:ok, %{status: status, body: resp_body}} ->
+        {:error, {:http, status, extract_error_message(resp_body)}}
+
+      {:error, reason} ->
+        {:error, {:request_failed, reason}}
+    end
+  end
+
+  @doc """
+  Updates an existing finance contact in Vereinfacht.
+
+  Only sends attributes that are typically synced from the member (name, email,
+  address fields). Returns the same contact_id on success.
+
+  ## Examples
+
+      iex> update_contact("242", member)
+      {:ok, "242"}
+
+      iex> update_contact("242", member)
+      {:error, {:http, 404, "Not Found"}}
+  """
+  @spec update_contact(String.t(), struct()) :: {:ok, String.t()} | {:error, term()}
+  def update_contact(contact_id, member) when is_binary(contact_id) do
+    base_url = base_url()
+    api_key = api_key()
+
+    if is_nil(base_url) or is_nil(api_key) do
+      {:error, :not_configured}
+    else
+      body = build_update_body(contact_id, member)
+      encoded_body = Jason.encode!(body)
+
+      url =
+        base_url
+        |> String.trim_trailing("/")
+        |> then(&"#{&1}/finance-contacts/#{contact_id}")
+
+      case Req.patch(
+             url,
+             [
+               body: encoded_body,
+               headers: headers(api_key)
+             ] ++ req_http_options()
+           ) do
+        {:ok, %{status: 200, body: _resp_body}} ->
+          {:ok, contact_id}
+
+        {:ok, %{status: status, body: body}} ->
+          {:error, {:http, status, extract_error_message(body)}}
+
+        {:error, reason} ->
+          {:error, {:request_failed, reason}}
+      end
+    end
+  end
+
+  @doc """
+  Finds a finance contact by email (GET /finance-contacts, then match in response).
+
+  The Vereinfacht API does not allow filter by email on this endpoint, so we
+  fetch the first page and find the contact client-side. Returns {:ok, contact_id}
+  if a contact with that email exists, {:error, :not_found} if none, or
+  {:error, reason} on API/network failure. Used before create for idempotency.
+  """
+  @spec find_contact_by_email(String.t()) :: {:ok, String.t()} | {:error, :not_found | term()}
+  def find_contact_by_email(email) when is_binary(email) do
+    if is_nil(base_url()) or is_nil(api_key()) or is_nil(club_id()) do
+      {:error, :not_configured}
+    else
+      do_find_contact_by_email(email)
+    end
+  end
+
+  @find_contact_page_size 100
+  @find_contact_max_pages 100
+
+  defp do_find_contact_by_email(email) do
+    normalized = String.trim(email) |> String.downcase()
+    do_find_contact_by_email_page(1, normalized)
+  end
+
+  defp do_find_contact_by_email_page(page, _normalized) when page > @find_contact_max_pages do
+    {:error, :not_found}
+  end
+
+  defp do_find_contact_by_email_page(page, normalized) do
+    base = base_url() |> String.trim_trailing("/") |> then(&"#{&1}/finance-contacts")
+    url = base <> "?page[size]=#{@find_contact_page_size}&page[number]=#{page}"
+
+    case Req.get(url, [headers: headers(api_key())] ++ req_http_options()) do
+      {:ok, %{status: 200, body: body}} when is_map(body) ->
+        handle_find_contact_page_response(body, page, normalized)
+
+      {:ok, %{status: status, body: body}} ->
+        {:error, {:http, status, extract_error_message(body)}}
+
+      {:error, reason} ->
+        {:error, {:request_failed, reason}}
+    end
+  end
+
+  defp handle_find_contact_page_response(body, page, normalized) do
+    case find_contact_id_by_email_in_list(body, normalized) do
+      id when is_binary(id) -> {:ok, id}
+      nil -> maybe_find_contact_next_page(body, page, normalized)
+    end
+  end
+
+  defp maybe_find_contact_next_page(body, page, normalized) do
+    data = Map.get(body, "data") || []
+
+    if length(data) < @find_contact_page_size,
+      do: {:error, :not_found},
+      else: do_find_contact_by_email_page(page + 1, normalized)
+  end
+
+  defp find_contact_id_by_email_in_list(%{"data" => list}, normalized) when is_list(list) do
+    Enum.find_value(list, fn
+      %{"id" => id, "attributes" => %{"email" => att_email, "isExternal" => true}}
+      when is_binary(att_email) ->
+        if att_email |> String.trim() |> String.downcase() == normalized do
+          normalize_contact_id(id)
+        else
+          nil
+        end
+
+      %{"id" => id, "attributes" => %{"email" => att_email, "isExternal" => "true"}}
+      when is_binary(att_email) ->
+        if att_email |> String.trim() |> String.downcase() == normalized do
+          normalize_contact_id(id)
+        else
+          nil
+        end
+
+      %{"id" => _id, "attributes" => _} ->
+        nil
+
+      _ ->
+        nil
+    end)
+  end
+
+  defp find_contact_id_by_email_in_list(_, _), do: nil
+
+  defp normalize_contact_id(id) when is_binary(id), do: id
+  defp normalize_contact_id(id) when is_integer(id), do: to_string(id)
+  defp normalize_contact_id(_), do: nil
+
+  @doc """
+  Fetches a single finance contact from Vereinfacht (GET /finance-contacts/:id).
+
+  Returns the full response body (decoded JSON) for debugging/display.
+  """
+  @spec get_contact(String.t()) :: {:ok, map()} | {:error, term()}
+  def get_contact(contact_id) when is_binary(contact_id) do
+    fetch_contact(contact_id, [])
+  end
+
+  @doc """
+  Fetches a finance contact with receipts (GET /finance-contacts/:id?include=receipts).
+
+  Returns {:ok, receipts} where receipts is a list of maps with :id and :attributes
+  (and optional :type) for each receipt, or {:error, reason}.
+  """
+  @spec get_contact_with_receipts(String.t()) :: {:ok, [map()]} | {:error, term()}
+  def get_contact_with_receipts(contact_id) when is_binary(contact_id) do
+    case fetch_contact(contact_id, include: "receipts") do
+      {:ok, body} -> {:ok, extract_receipts_from_response(body)}
+      {:error, _} = err -> err
+    end
+  end
+
+  defp fetch_contact(contact_id, query_params) do
+    base_url = base_url()
+    api_key = api_key()
+
+    if is_nil(base_url) or is_nil(api_key) do
+      {:error, :not_configured}
+    else
+      path =
+        base_url |> String.trim_trailing("/") |> then(&"#{&1}/finance-contacts/#{contact_id}")
+
+      url = build_url_with_params(path, query_params)
+
+      case Req.get(url, [headers: headers(api_key)] ++ req_http_options()) do
+        {:ok, %{status: 200, body: body}} when is_map(body) ->
+          {:ok, body}
+
+        {:ok, %{status: status, body: body}} ->
+          {:error, {:http, status, extract_error_message(body)}}
+
+        {:error, reason} ->
+          {:error, {:request_failed, reason}}
+      end
+    end
+  end
+
+  defp build_url_with_params(base, []), do: base
+
+  defp build_url_with_params(base, include: value) do
+    sep = if String.contains?(base, "?"), do: "&", else: "?"
+    base <> sep <> "include=" <> URI.encode(value, &URI.char_unreserved?/1)
+  end
+
+  # Allowlist of receipt attribute keys we expose (avoids String.to_atom on arbitrary API input / DoS).
+  @receipt_attr_allowlist ~w[amount bookingDate createdAt receiptType referenceNumber status updatedAt]a
+
+  defp extract_receipts_from_response(%{"included" => included}) when is_list(included) do
+    included
+    |> Enum.filter(&match?(%{"type" => "receipts"}, &1))
+    |> Enum.map(fn %{"id" => id, "attributes" => attrs} = r ->
+      Map.merge(%{id: id, type: r["type"]}, receipt_attrs_allowlist(attrs || %{}))
+    end)
+  end
+
+  defp extract_receipts_from_response(_), do: []
+
+  defp receipt_attrs_allowlist(attrs) when is_map(attrs) do
+    Map.new(@receipt_attr_allowlist, fn key ->
+      str_key = to_string(key)
+      {key, Map.get(attrs, str_key)}
+    end)
+    |> Enum.reject(fn {_k, v} -> is_nil(v) end)
+    |> Map.new()
+  end
+
+  defp base_url, do: Mv.Config.vereinfacht_api_url()
+  defp api_key, do: Mv.Config.vereinfacht_api_key()
+  defp club_id, do: Mv.Config.vereinfacht_club_id()
+
+  defp headers(api_key) do
+    [
+      {"Accept", @content_type},
+      {"Content-Type", @content_type},
+      {"Authorization", "Bearer #{api_key}"}
+    ]
+  end
+
+  defp build_create_body(member, club_id) do
+    attributes = member_to_attributes(member)
+
+    %{
+      "data" => %{
+        "type" => "finance-contacts",
+        "attributes" => attributes,
+        "relationships" => %{
+          "club" => %{
+            "data" => %{"type" => "clubs", "id" => club_id}
+          }
+        }
+      }
+    }
+  end
+
+  defp build_update_body(contact_id, member) do
+    attributes = member_to_attributes(member)
+
+    %{
+      "data" => %{
+        "type" => "finance-contacts",
+        "id" => contact_id,
+        "attributes" => attributes
+      }
+    }
+  end
+
+  defp member_to_attributes(member) do
+    address =
+      [member |> Map.get(:street), member |> Map.get(:house_number)]
+      |> Enum.reject(&is_nil/1)
+      |> Enum.map_join(" ", &to_string/1)
+      |> then(fn s -> if s == "", do: nil, else: s end)
+
+    %{}
+    |> put_attr("lastName", member |> Map.get(:last_name))
+    |> put_attr("firstName", member |> Map.get(:first_name))
+    |> put_attr("email", member |> Map.get(:email))
+    |> put_attr("address", address)
+    |> put_attr("zipCode", member |> Map.get(:postal_code))
+    |> put_attr("city", member |> Map.get(:city))
+    |> Map.put("contactType", "person")
+    |> Map.put("isExternal", true)
+    |> Enum.reject(fn {_k, v} -> is_nil(v) end)
+    |> Map.new()
+  end
+
+  defp put_attr(acc, _key, nil), do: acc
+  defp put_attr(acc, key, value), do: Map.put(acc, key, to_string(value))
+
+  defp get_contact_id_from_response(%{"data" => %{"id" => id}}) when is_binary(id), do: id
+
+  defp get_contact_id_from_response(%{"data" => %{"id" => id}}) when is_integer(id),
+    do: to_string(id)
+
+  defp get_contact_id_from_response(_), do: nil
+
+  defp extract_error_message(%{"errors" => [%{"detail" => d} | _]}) when is_binary(d), do: d
+  defp extract_error_message(%{"errors" => [%{"title" => t} | _]}) when is_binary(t), do: t
+  defp extract_error_message(body) when is_map(body), do: inspect(body)
+  defp extract_error_message(other), do: inspect(other)
+end
diff --git a/lib/mv/vereinfacht/sync_flash.ex b/lib/mv/vereinfacht/sync_flash.ex
new file mode 100644
index 0000000..874a717
--- /dev/null
+++ b/lib/mv/vereinfacht/sync_flash.ex
@@ -0,0 +1,46 @@
+defmodule Mv.Vereinfacht.SyncFlash do
+  @moduledoc """
+  Short-lived store for Vereinfacht sync results so the UI can show them after save.
+
+  The SyncContact change runs in after_transaction and cannot access the LiveView
+  socket. This module stores a message keyed by member_id; the form LiveView
+  calls `take/1` after a successful save and displays the message in flash.
+  """
+  @table :vereinfacht_sync_flash
+
+  @doc """
+  Stores a sync result for the given member. Overwrites any previous message.
+
+  - `:ok` - Sync succeeded (optional user message).
+  - `:warning` - Sync failed; message should be shown as a warning.
+  """
+  @spec store(String.t(), :ok | :warning, String.t()) :: :ok
+  def store(member_id, kind, message) when is_binary(member_id) do
+    :ets.insert(@table, {member_id, {kind, message}})
+    :ok
+  end
+
+  @doc """
+  Takes and removes the stored sync message for the given member.
+
+  Returns `{kind, message}` if present, otherwise `nil`.
+  """
+  @spec take(String.t()) :: {:ok | :warning, String.t()} | nil
+  def take(member_id) when is_binary(member_id) do
+    case :ets.take(@table, member_id) do
+      [{^member_id, value}] -> value
+      [] -> nil
+    end
+  end
+
+  @doc false
+  def create_table! do
+    # :public so any process can write (SyncContact runs in LiveView/Ash transaction process,
+    # not the process that created the table). :protected would restrict writes to the creating process.
+    if :ets.whereis(@table) == :undefined do
+      :ets.new(@table, [:set, :public, :named_table])
+    end
+
+    :ok
+  end
+end
diff --git a/lib/mv/vereinfacht/vereinfacht.ex b/lib/mv/vereinfacht/vereinfacht.ex
new file mode 100644
index 0000000..ce8005d
--- /dev/null
+++ b/lib/mv/vereinfacht/vereinfacht.ex
@@ -0,0 +1,165 @@
+defmodule Mv.Vereinfacht do
+  @moduledoc """
+  Business logic for Vereinfacht accounting software integration.
+
+  - `sync_member/1` – Sync a single member to the API (create or update contact).
+    Used by Member create/update (SyncContact) and by User actions that update
+    the linked member's email via Ecto (e.g. user email change).
+  - `sync_members_without_contact/0` – Bulk sync of members without a contact ID.
+  """
+  require Ash.Query
+  import Ash.Expr
+  alias Mv.Vereinfacht.Client
+  alias Mv.Membership.Member
+  alias Mv.Helpers.SystemActor
+  alias Mv.Helpers
+
+  @doc """
+  Syncs a single member to Vereinfacht (create or update finance contact).
+
+  If the member has no `vereinfacht_contact_id`, creates a contact and updates
+  the member with the new ID. If they already have an ID, updates the contact.
+  Uses system actor for any Ash update. Does nothing if Vereinfacht is not configured.
+
+  Returns:
+  - `:ok` – Contact was updated.
+  - `{:ok, member}` – Contact was created and member was updated with the new ID.
+  - `{:error, reason}` – API or update failed.
+  """
+  @spec sync_member(struct()) :: :ok | {:ok, struct()} | {:error, term()}
+  def sync_member(member) do
+    if Mv.Config.vereinfacht_configured?() do
+      do_sync_member(member)
+    else
+      :ok
+    end
+  end
+
+  defp do_sync_member(member) do
+    if present_contact_id?(member.vereinfacht_contact_id) do
+      sync_existing_contact(member)
+    else
+      ensure_contact_then_save(member)
+    end
+  end
+
+  defp sync_existing_contact(member) do
+    case Client.update_contact(member.vereinfacht_contact_id, member) do
+      {:ok, _} -> :ok
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp ensure_contact_then_save(member) do
+    case get_or_create_contact_id(member) do
+      {:ok, contact_id} -> save_contact_id(member, contact_id)
+      {:error, _} = err -> err
+    end
+  end
+
+  # Before create: find by email to avoid duplicate contacts (idempotency).
+  # When an existing contact is found, update it with current member data.
+  defp get_or_create_contact_id(member) do
+    email = member |> Map.get(:email) |> to_string() |> String.trim()
+
+    if email == "" do
+      Client.create_contact(member)
+    else
+      case Client.find_contact_by_email(email) do
+        {:ok, existing_id} -> update_existing_contact_and_return_id(existing_id, member)
+        {:error, :not_found} -> Client.create_contact(member)
+        {:error, _} = err -> err
+      end
+    end
+  end
+
+  defp update_existing_contact_and_return_id(contact_id, member) do
+    case Client.update_contact(contact_id, member) do
+      {:ok, _} -> {:ok, contact_id}
+      {:error, _} = err -> err
+    end
+  end
+
+  defp save_contact_id(member, contact_id) do
+    system_actor = SystemActor.get_system_actor()
+    opts = Helpers.ash_actor_opts(system_actor)
+
+    case Ash.update(member, %{vereinfacht_contact_id: contact_id}, [
+           {:action, :set_vereinfacht_contact_id} | opts
+         ]) do
+      {:ok, updated} -> {:ok, updated}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp present_contact_id?(nil), do: false
+  defp present_contact_id?(""), do: false
+  defp present_contact_id?(s) when is_binary(s), do: String.trim(s) != ""
+  defp present_contact_id?(_), do: false
+
+  @doc """
+  Formats an API/request error reason into a short user-facing message.
+
+  Used by SyncContact (flash) and GlobalSettingsLive (sync result list).
+  """
+  @spec format_error(term()) :: String.t()
+  def format_error({:http, _status, detail}) when is_binary(detail), do: "Vereinfacht: " <> detail
+  def format_error({:http, status, _}), do: "Vereinfacht: API error (HTTP #{status})."
+
+  def format_error({:request_failed, _}),
+    do: "Vereinfacht: Request failed (e.g. connection error)."
+
+  def format_error({:invalid_response, _}), do: "Vereinfacht: Invalid API response."
+  def format_error(other), do: "Vereinfacht: " <> inspect(other)
+
+  @doc """
+  Creates Vereinfacht contacts for all members that do not yet have a
+  `vereinfacht_contact_id`. Uses system actor for reads and updates.
+
+  Returns `{:ok, %{synced: count, errors: list}}` where errors is a list of
+  `{member_id, reason}`. Does nothing if Vereinfacht is not configured.
+  """
+  @spec sync_members_without_contact() ::
+          {:ok, %{synced: non_neg_integer(), errors: [{String.t(), term()}]}}
+          | {:error, :not_configured}
+  def sync_members_without_contact do
+    if Mv.Config.vereinfacht_configured?() do
+      system_actor = SystemActor.get_system_actor()
+      opts = Helpers.ash_actor_opts(system_actor)
+
+      query =
+        Member
+        |> Ash.Query.filter(
+          expr(is_nil(^ref(:vereinfacht_contact_id)) or ^ref(:vereinfacht_contact_id) == "")
+        )
+
+      case Ash.read(query, opts) do
+        {:ok, members} ->
+          do_sync_members(members, opts)
+
+        {:error, _} = err ->
+          err
+      end
+    else
+      {:error, :not_configured}
+    end
+  end
+
+  defp do_sync_members(members, opts) do
+    {synced, errors} =
+      Enum.reduce(members, {0, []}, fn member, {acc_synced, acc_errors} ->
+        {inc, new_errors} = sync_one_member(member, opts)
+        {acc_synced + inc, acc_errors ++ new_errors}
+      end)
+
+    {:ok, %{synced: synced, errors: errors}}
+  end
+
+  defp sync_one_member(member, _opts) do
+    case sync_member(member) do
+      :ok -> {1, []}
+      {:ok, _} -> {1, []}
+      {:error, reason} -> {0, [{member.id, reason}]}
+    end
+  end
+end
diff --git a/lib/mv_web/live/global_settings_live.ex b/lib/mv_web/live/global_settings_live.ex
index fafc955..b841931 100644
--- a/lib/mv_web/live/global_settings_live.ex
+++ b/lib/mv_web/live/global_settings_live.ex
@@ -23,6 +23,9 @@ defmodule MvWeb.GlobalSettingsLive do
   """
   use MvWeb, :live_view
 
+  require Ash.Query
+  import Ash.Expr
+
   alias Mv.Membership
 
   on_mount {MvWeb.LiveHelpers, :ensure_user_role_loaded}
@@ -41,11 +44,23 @@ defmodule MvWeb.GlobalSettingsLive do
       |> assign(:settings, settings)
       |> assign(:active_editing_section, nil)
       |> assign(:locale, locale)
+      |> assign(:vereinfacht_env_configured, Mv.Config.vereinfacht_env_configured?())
+      |> assign(:vereinfacht_api_url_env_set, Mv.Config.vereinfacht_api_url_env_set?())
+      |> assign(:vereinfacht_api_key_env_set, Mv.Config.vereinfacht_api_key_env_set?())
+      |> assign(:vereinfacht_club_id_env_set, Mv.Config.vereinfacht_club_id_env_set?())
+      |> assign(:vereinfacht_app_url_env_set, Mv.Config.vereinfacht_app_url_env_set?())
+      |> assign(:vereinfacht_api_key_set, present?(settings.vereinfacht_api_key))
+      |> assign(:last_vereinfacht_sync_result, nil)
       |> assign_form()
 
     {:ok, socket}
   end
 
+  defp present?(nil), do: false
+  defp present?(""), do: false
+  defp present?(s) when is_binary(s), do: String.trim(s) != ""
+  defp present?(_), do: false
+
   @impl true
   def render(assigns) do
     ~H"""
@@ -74,6 +89,98 @@ defmodule MvWeb.GlobalSettingsLive do
           </.button>
         </.form>
       </.form_section>
+      <%!-- Vereinfacht Integration Section --%>
+      <.form_section title={gettext("Vereinfacht Integration")}>
+        <%= if @vereinfacht_env_configured do %>
+          <p class="text-sm text-base-content/70 mb-4">
+            {gettext("Some values are set via environment variables. Those fields are read-only.")}
+          </p>
+        <% end %>
+        <.form for={@form} id="vereinfacht-form" phx-change="validate" phx-submit="save">
+          <div class="grid gap-4">
+            <.input
+              field={@form[:vereinfacht_api_url]}
+              type="text"
+              label={gettext("API URL")}
+              disabled={@vereinfacht_api_url_env_set}
+              placeholder={
+                if(@vereinfacht_api_url_env_set,
+                  do: gettext("From VEREINFACHT_API_URL"),
+                  else: "https://api.verein.visuel.dev/api/v1"
+                )
+              }
+            />
+            <div class="form-control">
+              <label class="label" for={@form[:vereinfacht_api_key].id}>
+                <span class="label-text">{gettext("API Key")}</span>
+                <%= if @vereinfacht_api_key_set do %>
+                  <span class="label-text-alt badge badge-ghost">{gettext("(set)")}</span>
+                <% end %>
+              </label>
+              <.input
+                field={@form[:vereinfacht_api_key]}
+                type="password"
+                label=""
+                disabled={@vereinfacht_api_key_env_set}
+                placeholder={
+                  if(@vereinfacht_api_key_env_set,
+                    do: gettext("From VEREINFACHT_API_KEY"),
+                    else:
+                      if(@vereinfacht_api_key_set,
+                        do: gettext("Leave blank to keep current"),
+                        else: nil
+                      )
+                  )
+                }
+              />
+            </div>
+            <.input
+              field={@form[:vereinfacht_club_id]}
+              type="text"
+              label={gettext("Club ID")}
+              disabled={@vereinfacht_club_id_env_set}
+              placeholder={
+                if(@vereinfacht_club_id_env_set, do: gettext("From VEREINFACHT_CLUB_ID"), else: "2")
+              }
+            />
+            <.input
+              field={@form[:vereinfacht_app_url]}
+              type="text"
+              label={gettext("App URL (contact view link)")}
+              disabled={@vereinfacht_app_url_env_set}
+              placeholder={
+                if(@vereinfacht_app_url_env_set,
+                  do: gettext("From VEREINFACHT_APP_URL"),
+                  else: "https://app.verein.visuel.dev"
+                )
+              }
+            />
+          </div>
+          <.button
+            :if={
+              not (@vereinfacht_api_url_env_set and @vereinfacht_api_key_env_set and
+                     @vereinfacht_club_id_env_set)
+            }
+            phx-disable-with={gettext("Saving...")}
+            variant="primary"
+            class="mt-2"
+          >
+            {gettext("Save Vereinfacht Settings")}
+          </.button>
+          <.button
+            :if={Mv.Config.vereinfacht_configured?()}
+            type="button"
+            phx-click="sync_vereinfacht_contacts"
+            phx-disable-with={gettext("Syncing...")}
+            class="mt-4 btn-outline"
+          >
+            {gettext("Sync all members without Vereinfacht contact")}
+          </.button>
+          <%= if @last_vereinfacht_sync_result do %>
+            <.vereinfacht_sync_result result={@last_vereinfacht_sync_result} />
+          <% end %>
+        </.form>
+      </.form_section>
       <%!-- Memberdata Section --%>
       <.form_section title={gettext("Memberdata")}>
         <.live_component
@@ -100,18 +207,54 @@ defmodule MvWeb.GlobalSettingsLive do
      assign(socket, form: AshPhoenix.Form.validate(socket.assigns.form, setting_params))}
   end
 
+  @impl true
+  def handle_event("sync_vereinfacht_contacts", _params, socket) do
+    case Mv.Vereinfacht.sync_members_without_contact() do
+      {:ok, %{synced: synced, errors: errors}} ->
+        errors_with_names = enrich_sync_errors(errors)
+        result = %{synced: synced, errors: errors_with_names}
+
+        socket =
+          socket
+          |> assign(:last_vereinfacht_sync_result, result)
+          |> put_flash(
+            :info,
+            if(errors_with_names == [],
+              do: gettext("Synced %{count} member(s) to Vereinfacht.", count: synced),
+              else:
+                gettext("Synced %{count} member(s). %{error_count} failed.",
+                  count: synced,
+                  error_count: length(errors_with_names)
+                )
+            )
+          )
+
+        {:noreply, socket}
+
+      {:error, :not_configured} ->
+        {:noreply,
+         put_flash(
+           socket,
+           :error,
+           gettext("Vereinfacht is not configured. Set API URL, API Key, and Club ID.")
+         )}
+    end
+  end
+
   @impl true
   def handle_event("save", %{"setting" => setting_params}, socket) do
     actor = MvWeb.LiveHelpers.current_actor(socket)
+    # Never send blank API key so we do not overwrite the stored secret (security)
+    setting_params_clean = drop_blank_vereinfacht_api_key(setting_params)
 
-    case MvWeb.LiveHelpers.submit_form(socket.assigns.form, setting_params, actor) do
+    case MvWeb.LiveHelpers.submit_form(socket.assigns.form, setting_params_clean, actor) do
       {:ok, _updated_settings} ->
-        # Reload settings from database to ensure all dependent data is updated
         {:ok, fresh_settings} = Membership.get_settings()
 
         socket =
           socket
           |> assign(:settings, fresh_settings)
+          |> assign(:vereinfacht_api_key_set, present?(fresh_settings.vereinfacht_api_key))
           |> put_flash(:info, gettext("Settings updated successfully"))
           |> assign_form()
 
@@ -122,6 +265,16 @@ defmodule MvWeb.GlobalSettingsLive do
     end
   end
 
+  defp drop_blank_vereinfacht_api_key(params) when is_map(params) do
+    case params do
+      %{"vereinfacht_api_key" => v} when v in [nil, ""] ->
+        Map.delete(params, "vereinfacht_api_key")
+
+      _ ->
+        params
+    end
+  end
+
   @impl true
   def handle_info({:custom_field_saved, _custom_field, action}, socket) do
     send_update(MvWeb.CustomFieldLive.IndexComponent,
@@ -202,9 +355,12 @@ defmodule MvWeb.GlobalSettingsLive do
   end
 
   defp assign_form(%{assigns: %{settings: settings}} = socket) do
+    # Never put API key into form/DOM to avoid secret leak in source or DevTools
+    settings_for_form = %{settings | vereinfacht_api_key: nil}
+
     form =
       AshPhoenix.Form.for_update(
-        settings,
+        settings_for_form,
         :update,
         api: Membership,
         as: "setting",
@@ -213,4 +369,74 @@ defmodule MvWeb.GlobalSettingsLive do
 
     assign(socket, form: to_form(form))
   end
+
+  defp enrich_sync_errors([]), do: []
+
+  defp enrich_sync_errors(errors) when is_list(errors) do
+    name_by_id = fetch_member_names_by_ids(Enum.map(errors, fn {id, _} -> id end))
+
+    Enum.map(errors, fn {member_id, reason} ->
+      %{
+        member_id: member_id,
+        member_name: Map.get(name_by_id, member_id) || to_string(member_id),
+        message: Mv.Vereinfacht.format_error(reason),
+        detail: extract_vereinfacht_detail(reason)
+      }
+    end)
+  end
+
+  defp fetch_member_names_by_ids(ids) do
+    actor = Mv.Helpers.SystemActor.get_system_actor()
+    opts = Mv.Helpers.ash_actor_opts(actor)
+    query = Ash.Query.filter(Mv.Membership.Member, expr(id in ^ids))
+
+    case Ash.read(query, opts) do
+      {:ok, members} ->
+        Map.new(members, fn m -> {m.id, MvWeb.Helpers.MemberHelpers.display_name(m)} end)
+
+      _ ->
+        %{}
+    end
+  end
+
+  defp extract_vereinfacht_detail({:http, _status, detail}) when is_binary(detail), do: detail
+  defp extract_vereinfacht_detail(_), do: nil
+
+  defp translate_vereinfacht_message(%{detail: detail}) when is_binary(detail) do
+    gettext("Vereinfacht: %{detail}",
+      detail: Gettext.dgettext(MvWeb.Gettext, "default", detail)
+    )
+  end
+
+  defp translate_vereinfacht_message(%{message: message}) do
+    Gettext.dgettext(MvWeb.Gettext, "default", message)
+  end
+
+  attr :result, :map, required: true
+
+  defp vereinfacht_sync_result(assigns) do
+    ~H"""
+    <div class="mt-4 p-4 rounded-lg border border-base-300 bg-base-200 space-y-2">
+      <p class="font-medium">
+        {gettext("Last sync result:")}
+        <span class="text-success-aa ml-1">{gettext("%{count} synced", count: @result.synced)}</span>
+        <%= if @result.errors != [] do %>
+          <span class="text-error-aa ml-1">
+            {gettext("%{count} failed", count: length(@result.errors))}
+          </span>
+        <% end %>
+      </p>
+      <%= if @result.errors != [] do %>
+        <p class="text-sm text-base-content/70 mt-2">{gettext("Failed members:")}</p>
+        <ul class="list-disc list-inside text-sm space-y-1 max-h-48 overflow-y-auto">
+          <%= for err <- @result.errors do %>
+            <li>
+              <span class="font-medium">{err.member_name}</span>: {translate_vereinfacht_message(err)}
+            </li>
+          <% end %>
+        </ul>
+      <% end %>
+    </div>
+    """
+  end
 end
diff --git a/lib/mv_web/live/member_live/form.ex b/lib/mv_web/live/member_live/form.ex
index f9588c0..7c138c4 100644
--- a/lib/mv_web/live/member_live/form.ex
+++ b/lib/mv_web/live/member_live/form.ex
@@ -319,11 +319,40 @@ defmodule MvWeb.MemberLive.Form do
     socket =
       socket
       |> put_flash(:info, flash_message)
+      |> maybe_put_vereinfacht_sync_flash(member.id)
       |> push_navigate(to: return_path(socket.assigns.return_to, member))
 
     {:noreply, socket}
   end
 
+  defp maybe_put_vereinfacht_sync_flash(socket, member_id) do
+    case Mv.Vereinfacht.SyncFlash.take(to_string(member_id)) do
+      {:warning, message} ->
+        put_flash(socket, :warning, translate_vereinfacht_flash(message))
+
+      {:ok, _message} ->
+        # Optionally show sync success; for now we keep only the main success message
+        socket
+
+      nil ->
+        socket
+    end
+  end
+
+  defp translate_vereinfacht_flash(message) when is_binary(message) do
+    prefix = "Vereinfacht: "
+
+    if String.starts_with?(message, prefix) do
+      detail = message |> String.trim_leading(prefix) |> String.trim()
+
+      Gettext.dgettext(MvWeb.Gettext, "default", "Vereinfacht: %{detail}",
+        detail: Gettext.dgettext(MvWeb.Gettext, "default", detail)
+      )
+    else
+      Gettext.dgettext(MvWeb.Gettext, "default", message)
+    end
+  end
+
   defp handle_save_error(socket, form) do
     # Always show a flash message when save fails
     # Field-level validation errors are displayed in form fields, but flash provides additional feedback
diff --git a/lib/mv_web/live/member_live/show.ex b/lib/mv_web/live/member_live/show.ex
index 47e8878..a85bf69 100644
--- a/lib/mv_web/live/member_live/show.ex
+++ b/lib/mv_web/live/member_live/show.ex
@@ -256,6 +256,7 @@ defmodule MvWeb.MemberLive.Show do
           id={"membership-fees-#{@member.id}"}
           member={@member}
           current_user={@current_user}
+          vereinfacht_receipts={@vereinfacht_receipts}
         />
       <% end %>
     </Layouts.app>
@@ -264,7 +265,10 @@ defmodule MvWeb.MemberLive.Show do
 
   @impl true
   def mount(_params, _session, socket) do
-    {:ok, assign(socket, :active_tab, :contact)}
+    {:ok,
+     socket
+     |> assign(:active_tab, :contact)
+     |> assign(:vereinfacht_receipts, nil)}
   end
 
   @impl true
@@ -316,6 +320,16 @@ defmodule MvWeb.MemberLive.Show do
     {:noreply, assign(socket, :active_tab, :membership_fees)}
   end
 
+  def handle_event("load_vereinfacht_receipts", %{"contact_id" => contact_id}, socket) do
+    response =
+      case Mv.Vereinfacht.Client.get_contact_with_receipts(contact_id) do
+        {:ok, receipts} -> {:ok, receipts}
+        {:error, reason} -> {:error, reason}
+      end
+
+    {:noreply, assign(socket, :vereinfacht_receipts, response)}
+  end
+
   # Flash set in LiveComponent is not shown in parent layout; child sends this to display flash
   @impl true
   def handle_info({:put_flash, type, message}, socket) do
diff --git a/lib/mv_web/live/member_live/show/membership_fees_component.ex b/lib/mv_web/live/member_live/show/membership_fees_component.ex
index 0739b5e..1ce6f77 100644
--- a/lib/mv_web/live/member_live/show/membership_fees_component.ex
+++ b/lib/mv_web/live/member_live/show/membership_fees_component.ex
@@ -50,6 +50,90 @@ defmodule MvWeb.MemberLive.Show.MembershipFeesComponent do
           <% end %>
         </div>
 
+        <%!-- Vereinfacht: contact info when synced, or warning when API is configured but no contact --%>
+        <%= if Mv.Config.vereinfacht_configured?() do %>
+          <%= if @vereinfacht_contact_present do %>
+            <div class="mb-4">
+              <div class="flex flex-col gap-2">
+                <.link
+                  :if={Mv.Config.vereinfacht_contact_view_url(@member.vereinfacht_contact_id)}
+                  href={Mv.Config.vereinfacht_contact_view_url(@member.vereinfacht_contact_id)}
+                  target="_blank"
+                  rel="noopener noreferrer"
+                  class="link link-accent underline inline-flex items-center gap-1 w-fit"
+                >
+                  {gettext("View contact in Vereinfacht")}
+                  <.icon name="hero-arrow-top-right-on-square" class="inline-block size-4" />
+                </.link>
+                <div>
+                  <button
+                    type="button"
+                    phx-click="load_vereinfacht_receipts"
+                    phx-value-contact_id={@member.vereinfacht_contact_id}
+                    class="btn btn-sm btn-ghost"
+                  >
+                    {gettext("Show bookings/receipts from Vereinfacht")}
+                  </button>
+                </div>
+                <%= if @vereinfacht_receipts do %>
+                  <div
+                    class="mt-2 rounded border border-base-300 bg-base-200 p-3 overflow-x-auto max-h-96 overflow-y-auto"
+                    tabindex="0"
+                    role="region"
+                    aria-label={gettext("Vereinfacht receipts")}
+                  >
+                    <%= if match?({:ok, _}, @vereinfacht_receipts) do %>
+                      <% {_, receipts} = @vereinfacht_receipts %>
+                      <%= if receipts == [] do %>
+                        <p class="text-sm text-base-content/70">{gettext("No receipts")}</p>
+                      <% else %>
+                        <% cols = receipt_display_columns(receipts) %>
+                        <table class="table table-xs table-pin-rows">
+                          <thead>
+                            <tr>
+                              <%= for {_key, translated_label} <- cols do %>
+                                <th>{translated_label}</th>
+                              <% end %>
+                            </tr>
+                          </thead>
+                          <tbody>
+                            <%= for r <- receipts do %>
+                              <tr>
+                                <%= for {col_key, _header_key} <- cols do %>
+                                  <td>{format_receipt_cell(col_key, r[col_key])}</td>
+                                <% end %>
+                              </tr>
+                            <% end %>
+                          </tbody>
+                        </table>
+                      <% end %>
+                    <% else %>
+                      <% {:error, reason} = @vereinfacht_receipts %>
+                      <p class="text-sm text-error">
+                        {gettext("Error loading receipts: %{reason}",
+                          reason: format_vereinfacht_error(reason)
+                        )}
+                      </p>
+                    <% end %>
+                  </div>
+                <% end %>
+              </div>
+            </div>
+          <% else %>
+            <div class="mb-4 rounded-lg border border-warning/50 bg-warning/10 p-3">
+              <p class="text-warning font-medium flex items-center gap-2">
+                <.icon name="hero-exclamation-triangle" class="size-5 shrink-0" />
+                {gettext("No Vereinfacht contact exists for this member.")}
+              </p>
+              <p class="text-sm text-base-content/70 mt-1">
+                {gettext(
+                  "Sync this member from Settings (Vereinfacht section) or save the member again to create the contact."
+                )}
+              </p>
+            </div>
+          <% end %>
+        <% end %>
+
         <%!-- Action Buttons (only when user has permission) --%>
         <div class="flex gap-2 mb-4">
           <.button
@@ -431,6 +515,7 @@ defmodule MvWeb.MemberLive.Show.MembershipFeesComponent do
      |> assign(:can_create_cycle, can_create_cycle)
      |> assign(:can_destroy_cycle, can_destroy_cycle)
      |> assign(:can_update_cycle, can_update_cycle)
+     |> assign(:vereinfacht_contact_present, present_contact_id?(member.vereinfacht_contact_id))
      |> assign_new(:interval_warning, fn -> nil end)
      |> assign_new(:editing_cycle, fn -> nil end)
      |> assign_new(:deleting_cycle, fn -> nil end)
@@ -439,7 +524,8 @@ defmodule MvWeb.MemberLive.Show.MembershipFeesComponent do
      |> assign_new(:creating_cycle, fn -> false end)
      |> assign_new(:create_cycle_date, fn -> nil end)
      |> assign_new(:create_cycle_error, fn -> nil end)
-     |> assign_new(:regenerating, fn -> false end)}
+     |> assign_new(:regenerating, fn -> false end)
+     |> assign_new(:vereinfacht_receipts, fn -> nil end)}
   end
 
   @impl true
@@ -997,6 +1083,142 @@ defmodule MvWeb.MemberLive.Show.MembershipFeesComponent do
 
   defp format_create_cycle_period(_date, _interval), do: ""
 
+  defp present_contact_id?(nil), do: false
+  defp present_contact_id?(id) when is_binary(id), do: String.trim(id) != ""
+  defp present_contact_id?(_), do: false
+
+  defp format_vereinfacht_error({:http, status, detail}) when is_binary(detail),
+    do: "HTTP #{status} – #{detail}"
+
+  defp format_vereinfacht_error({:http, status, _}), do: "HTTP #{status}"
+  defp format_vereinfacht_error(reason), do: inspect(reason)
+
+  # Ordered receipt columns: {api_key, gettext key for header}. Only columns present in data are shown.
+  @receipt_column_spec [
+    {:amount, "Amount"},
+    {:bookingDate, "Booking date"},
+    {:createdAt, "Created at"},
+    {:receiptType, "Receipt type"},
+    {:referenceNumber, "Reference number"},
+    {:status, "Status"},
+    {:updatedAt, "Updated at"}
+  ]
+
+  defp receipt_display_columns(receipts) when is_list(receipts) do
+    keys_in_data = receipts |> Enum.flat_map(&Map.keys/1) |> MapSet.new()
+
+    Enum.filter(@receipt_column_spec, fn {key, _} -> MapSet.member?(keys_in_data, key) end)
+    |> Enum.map(fn {key, msgid} -> {key, Gettext.gettext(MvWeb.Gettext, msgid)} end)
+  end
+
+  defp format_receipt_cell(:amount, nil), do: "—"
+
+  defp format_receipt_cell(:amount, val) when is_number(val) do
+    case Decimal.cast(val) do
+      {:ok, d} -> MembershipFeeHelpers.format_currency(d)
+      _ -> to_string(val)
+    end
+  end
+
+  defp format_receipt_cell(:amount, val) when is_binary(val) do
+    case Decimal.parse(val) do
+      {d, _} -> MembershipFeeHelpers.format_currency(d)
+      :error -> val
+    end
+  end
+
+  defp format_receipt_cell(:amount, val), do: to_string(val)
+
+  defp format_receipt_cell(:status, nil), do: "—"
+
+  defp format_receipt_cell(:status, val) when is_binary(val) do
+    translate_receipt_status(val)
+  end
+
+  defp format_receipt_cell(:status, val), do: translate_receipt_status(to_string(val))
+
+  defp format_receipt_cell(:receiptType, nil), do: "—"
+
+  defp format_receipt_cell(:receiptType, val) when is_binary(val) do
+    translate_receipt_type(val)
+  end
+
+  defp format_receipt_cell(:receiptType, val), do: translate_receipt_type(to_string(val))
+
+  defp format_receipt_cell(col_key, nil) when col_key in [:bookingDate, :createdAt, :updatedAt],
+    do: "—"
+
+  defp format_receipt_cell(col_key, val) when col_key in [:bookingDate, :createdAt, :updatedAt] do
+    format_receipt_date(val)
+  end
+
+  defp format_receipt_cell(_col_key, val) when is_binary(val), do: val
+  defp format_receipt_cell(_col_key, val) when is_number(val), do: to_string(val)
+
+  defp format_receipt_cell(_col_key, val) when is_boolean(val),
+    do: if(val, do: gettext("Yes"), else: gettext("No"))
+
+  defp format_receipt_cell(_col_key, %Date{} = d), do: format_receipt_date_short(d)
+  defp format_receipt_cell(_col_key, val) when is_map(val) or is_list(val), do: Jason.encode!(val)
+  defp format_receipt_cell(_col_key, val), do: to_string(val)
+
+  defp format_receipt_date(%Date{} = d), do: format_receipt_date_short(d)
+
+  defp format_receipt_date(val) when is_binary(val) do
+    case parse_receipt_date(val) do
+      {:ok, d} -> format_receipt_date_short(d)
+      _ -> val
+    end
+  end
+
+  defp format_receipt_date(val), do: to_string(val)
+
+  # Parses ISO date or datetime string to Date (uses first 10 chars for datetime strings)
+  defp parse_receipt_date(val) when is_binary(val) do
+    date_str = if String.length(val) >= 10, do: String.slice(val, 0, 10), else: val
+    Date.from_iso8601(date_str)
+  end
+
+  # Format as "12. Dez. 2025" (day. abbreviated month. year) with translated month
+  defp format_receipt_date_short(%Date{day: day, month: month, year: year}) do
+    "#{day}. #{receipt_month_abbr(month)} #{year}"
+  end
+
+  defp receipt_month_abbr(1), do: gettext("Jan.")
+  defp receipt_month_abbr(2), do: gettext("Feb.")
+  defp receipt_month_abbr(3), do: gettext("Mar.")
+  defp receipt_month_abbr(4), do: gettext("Apr.")
+  defp receipt_month_abbr(5), do: gettext("May")
+  defp receipt_month_abbr(6), do: gettext("Jun.")
+  defp receipt_month_abbr(7), do: gettext("Jul.")
+  defp receipt_month_abbr(8), do: gettext("Aug.")
+  defp receipt_month_abbr(9), do: gettext("Sep.")
+  defp receipt_month_abbr(10), do: gettext("Oct.")
+  defp receipt_month_abbr(11), do: gettext("Nov.")
+  defp receipt_month_abbr(12), do: gettext("Dec.")
+  defp receipt_month_abbr(_), do: ""
+
+  # Translate API status values for display (extend as API returns more values)
+  defp translate_receipt_status("paid"), do: gettext("Paid")
+  defp translate_receipt_status("unpaid"), do: gettext("Unpaid")
+  defp translate_receipt_status("suspended"), do: gettext("Suspended")
+  defp translate_receipt_status("open"), do: gettext("Open")
+  defp translate_receipt_status("cancelled"), do: gettext("Cancelled")
+  defp translate_receipt_status("draft"), do: gettext("Draft")
+  defp translate_receipt_status("incompleted"), do: gettext("Incompleted")
+  defp translate_receipt_status("completed"), do: gettext("Completed")
+  defp translate_receipt_status("empty"), do: "—"
+  defp translate_receipt_status(other), do: other
+
+  # Translate API receipt type values (extend as API returns more values)
+  defp translate_receipt_type("invoice"), do: gettext("Invoice")
+  defp translate_receipt_type("receipt"), do: gettext("Receipt")
+  defp translate_receipt_type("credit_note"), do: gettext("Credit note")
+  defp translate_receipt_type("credit"), do: gettext("Credit")
+  defp translate_receipt_type("expense"), do: gettext("Expense")
+  defp translate_receipt_type("income"), do: gettext("Income")
+  defp translate_receipt_type(other), do: other
+
   # Helper component for section box
   attr :title, :string, required: true
   slot :inner_block, required: true
diff --git a/priv/gettext/de/LC_MESSAGES/default.po b/priv/gettext/de/LC_MESSAGES/default.po
index b7145f0..d39d86b 100644
--- a/priv/gettext/de/LC_MESSAGES/default.po
+++ b/priv/gettext/de/LC_MESSAGES/default.po
@@ -200,6 +200,7 @@ msgstr "Straße"
 #: lib/mv_web/live/member_field_live/index_component.ex
 #: lib/mv_web/live/member_live/index/formatter.ex
 #: lib/mv_web/live/member_live/show.ex
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
 #: lib/mv_web/live/role_live/show.ex
 #, elixir-autogen, elixir-format
 msgid "No"
@@ -2622,3 +2623,291 @@ msgstr "Der Wertetyp kann nach dem Erstellen nicht mehr geändert werden."
 #, elixir-autogen, elixir-format, fuzzy
 msgid "Could not load member list. Please try again."
 msgstr "Mitgliederliste konnte nicht geladen werden. Bitte versuche es erneut."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API Key"
+msgstr "API-Schlüssel"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API URL"
+msgstr "API-URL"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Club ID"
+msgstr "Vereins-ID"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_KEY"
+msgstr "Aus VEREINFACHT_API_KEY"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_URL"
+msgstr "Aus VEREINFACHT_API_URL"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_CLUB_ID"
+msgstr "Aus VEREINFACHT_CLUB_ID"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Save Vereinfacht Settings"
+msgstr "Vereinfacht-Einstellungen speichern"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Sync all members without Vereinfacht contact"
+msgstr "Alle Mitglieder ohne Vereinfacht-Kontakt synchronisieren"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Synced %{count} member(s) to Vereinfacht."
+msgstr "%{count} Mitglied(er) mit Vereinfacht synchronisiert."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Syncing..."
+msgstr "Synchronisiere..."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht Integration"
+msgstr "Vereinfacht-Integration"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht is not configured. Set API URL, API Key, and Club ID."
+msgstr "Vereinfacht ist nicht konfiguriert. Bitte setze API-URL, API-Schlüssel und Vereins-ID."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "View contact in Vereinfacht"
+msgstr "Kontakt in Vereinfacht anzeigen"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} failed"
+msgstr "%{count} fehlgeschlagen"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} synced"
+msgstr "%{count} synchronisiert"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Failed members:"
+msgstr "Fehlgeschlagene Mitglieder:"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Last sync result:"
+msgstr "Letztes Sync-Ergebnis:"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Synced %{count} member(s). %{error_count} failed."
+msgstr "%{count} Mitglied(er) synchronisiert. %{error_count} Fehler."
+
+# Vereinfacht API error messages (translated for UI)
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht: %{detail}"
+msgstr "Vereinfacht: %{detail}"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No Vereinfacht contact exists for this member."
+msgstr "Für dieses Mitglied existiert kein Vereinfacht-Kontakt."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sync this member from Settings (Vereinfacht section) or save the member again to create the contact."
+msgstr "Synchronisiere dieses Mitglied unter Einstellungen (Bereich Vereinfacht) oder speichere das Mitglied erneut, um den Kontakt anzulegen."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "(set)"
+msgstr "(gesetzt)"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Leave blank to keep current"
+msgstr "Leer lassen, um den aktuellen Wert beizubehalten"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Some values are set via environment variables. Those fields are read-only."
+msgstr "Einige Werte werden über Umgebungsvariablen gesetzt. Diese Felder sind schreibgeschützt."
+
+# Vereinfacht API validation messages (looked up at runtime via dgettext)
+msgid "The address field is required."
+msgstr "Das Adressfeld ist erforderlich."
+
+msgid "The city field is required."
+msgstr "Das Stadtfeld ist erforderlich."
+
+msgid "The email field is required."
+msgstr "Das E-Mail-Feld ist erforderlich."
+
+msgid "The first name field is required."
+msgstr "Das Vornamenfeld ist erforderlich."
+
+msgid "The last name field is required."
+msgstr "Das Nachnamenfeld ist erforderlich."
+
+msgid "The zip code field is required."
+msgstr "Das Postleitzahlenfeld ist erforderlich."
+
+msgid "Too Many Attempts."
+msgstr "Zu viele Versuche."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "App URL (contact view link)"
+msgstr "App-URL (Link zur Kontaktansicht)"
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "From VEREINFACHT_APP_URL"
+msgstr "Aus VEREINFACHT_APP_URL"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Error loading receipts: %{reason}"
+msgstr "Belege konnten nicht geladen werden: %{reason}"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No receipts"
+msgstr "Keine Belege"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Show bookings/receipts from Vereinfacht"
+msgstr "Buchungen/Belege aus Vereinfacht anzeigen"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht receipts"
+msgstr "Vereinfacht-Belege"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Cancelled"
+msgstr "Storniert"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit"
+msgstr "Gutschrift"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit note"
+msgstr "Gutschrift"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Draft"
+msgstr "Entwurf"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Invoice"
+msgstr "Rechnung"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Open"
+msgstr "Offen"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Receipt"
+msgstr "Beleg"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Apr."
+msgstr "Apr."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Aug."
+msgstr "Aug."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Completed"
+msgstr "Abgeschlossen"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Dec."
+msgstr "Dez."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Expense"
+msgstr "Ausgabe"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Feb."
+msgstr "Feb."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Income"
+msgstr "Einnahme"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Incompleted"
+msgstr "Unvollständig"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jan."
+msgstr "Jan."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jul."
+msgstr "Jul."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jun."
+msgstr "Jun."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Mar."
+msgstr "Mär."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "May"
+msgstr "Mai"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Nov."
+msgstr "Nov."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Oct."
+msgstr "Okt."
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sep."
+msgstr "Sep."
diff --git a/priv/gettext/default.pot b/priv/gettext/default.pot
index c1aafd9..ff466ab 100644
--- a/priv/gettext/default.pot
+++ b/priv/gettext/default.pot
@@ -201,6 +201,7 @@ msgstr ""
 #: lib/mv_web/live/member_field_live/index_component.ex
 #: lib/mv_web/live/member_live/index/formatter.ex
 #: lib/mv_web/live/member_live/show.ex
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
 #: lib/mv_web/live/role_live/show.ex
 #, elixir-autogen, elixir-format
 msgid "No"
@@ -2623,3 +2624,290 @@ msgstr ""
 #, elixir-autogen, elixir-format
 msgid "Could not load member list. Please try again."
 msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API Key"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API URL"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Club ID"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_KEY"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_URL"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_CLUB_ID"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Save Vereinfacht Settings"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Sync all members without Vereinfacht contact"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Synced %{count} member(s) to Vereinfacht."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Syncing..."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht Integration"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht is not configured. Set API URL, API Key, and Club ID."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "View contact in Vereinfacht"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} failed"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} synced"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Failed members:"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Last sync result:"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Synced %{count} member(s). %{error_count} failed."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht: %{detail}"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No Vereinfacht contact exists for this member."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sync this member from Settings (Vereinfacht section) or save the member again to create the contact."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "(set)"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Leave blank to keep current"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Some values are set via environment variables. Those fields are read-only."
+msgstr ""
+
+# Vereinfacht API validation messages (looked up at runtime via dgettext)
+msgid "The address field is required."
+msgstr ""
+
+msgid "The city field is required."
+msgstr ""
+
+msgid "The email field is required."
+msgstr ""
+
+msgid "The first name field is required."
+msgstr ""
+
+msgid "The last name field is required."
+msgstr ""
+
+msgid "The zip code field is required."
+msgstr ""
+
+msgid "Too Many Attempts."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "App URL (contact view link)"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_APP_URL"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Error loading receipts: %{reason}"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No receipts"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Show bookings/receipts from Vereinfacht"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht receipts"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Cancelled"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit note"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Draft"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Invoice"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Open"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Receipt"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Apr."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Aug."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Completed"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Dec."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Expense"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Feb."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Income"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Incompleted"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jan."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jul."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jun."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Mar."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "May"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Nov."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Oct."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sep."
+msgstr ""
diff --git a/priv/gettext/en/LC_MESSAGES/default.po b/priv/gettext/en/LC_MESSAGES/default.po
index 12c1666..e5e0181 100644
--- a/priv/gettext/en/LC_MESSAGES/default.po
+++ b/priv/gettext/en/LC_MESSAGES/default.po
@@ -201,6 +201,7 @@ msgstr ""
 #: lib/mv_web/live/member_field_live/index_component.ex
 #: lib/mv_web/live/member_live/index/formatter.ex
 #: lib/mv_web/live/member_live/show.ex
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
 #: lib/mv_web/live/role_live/show.ex
 #, elixir-autogen, elixir-format
 msgid "No"
@@ -2623,3 +2624,290 @@ msgstr ""
 #, elixir-autogen, elixir-format, fuzzy
 msgid "Could not load member list. Please try again."
 msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API Key"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "API URL"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Club ID"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_KEY"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_API_URL"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "From VEREINFACHT_CLUB_ID"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Save Vereinfacht Settings"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Sync all members without Vereinfacht contact"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Synced %{count} member(s) to Vereinfacht."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Syncing..."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht Integration"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Vereinfacht is not configured. Set API URL, API Key, and Club ID."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "View contact in Vereinfacht"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} failed"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "%{count} synced"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Failed members:"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Last sync result:"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Synced %{count} member(s). %{error_count} failed."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Vereinfacht: %{detail}"
+msgstr "Vereinfacht: %{detail}"
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No Vereinfacht contact exists for this member."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sync this member from Settings (Vereinfacht section) or save the member again to create the contact."
+msgstr "Sync this member from Settings (Vereinfacht section) or save the member again to create the contact."
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "(set)"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Leave blank to keep current"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "Some values are set via environment variables. Those fields are read-only."
+msgstr ""
+
+# Vereinfacht API validation messages (looked up at runtime via dgettext)
+msgid "The address field is required."
+msgstr ""
+
+msgid "The city field is required."
+msgstr ""
+
+msgid "The email field is required."
+msgstr ""
+
+msgid "The first name field is required."
+msgstr ""
+
+msgid "The last name field is required."
+msgstr ""
+
+msgid "The zip code field is required."
+msgstr ""
+
+msgid "Too Many Attempts."
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format
+msgid "App URL (contact view link)"
+msgstr ""
+
+#: lib/mv_web/live/global_settings_live.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "From VEREINFACHT_APP_URL"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Error loading receipts: %{reason}"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "No receipts"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Show bookings/receipts from Vereinfacht"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Vereinfacht receipts"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Cancelled"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Credit note"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Draft"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Invoice"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Open"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Receipt"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Apr."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Aug."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Completed"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Dec."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Expense"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Feb."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Income"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Incompleted"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jan."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jul."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Jun."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Mar."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "May"
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Nov."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Oct."
+msgstr ""
+
+#: lib/mv_web/live/member_live/show/membership_fees_component.ex
+#, elixir-autogen, elixir-format
+msgid "Sep."
+msgstr ""
diff --git a/priv/repo/migrations/20260218185510_add_vereinfacht_contact_id_to_members.exs b/priv/repo/migrations/20260218185510_add_vereinfacht_contact_id_to_members.exs
new file mode 100644
index 0000000..b8bc8b4
--- /dev/null
+++ b/priv/repo/migrations/20260218185510_add_vereinfacht_contact_id_to_members.exs
@@ -0,0 +1,21 @@
+defmodule Mv.Repo.Migrations.AddVereinfachtContactIdToMembers do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:members) do
+      add :vereinfacht_contact_id, :text
+    end
+  end
+
+  def down do
+    alter table(:members) do
+      remove :vereinfacht_contact_id
+    end
+  end
+end
diff --git a/priv/repo/migrations/20260218185541_add_vereinfacht_settings.exs b/priv/repo/migrations/20260218185541_add_vereinfacht_settings.exs
new file mode 100644
index 0000000..72aac60
--- /dev/null
+++ b/priv/repo/migrations/20260218185541_add_vereinfacht_settings.exs
@@ -0,0 +1,25 @@
+defmodule Mv.Repo.Migrations.AddVereinfachtSettings do
+  @moduledoc """
+  Updates resources based on their most recent snapshots.
+
+  This file was autogenerated with `mix ash_postgres.generate_migrations`
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:settings) do
+      add :vereinfacht_api_url, :text
+      add :vereinfacht_api_key, :text
+      add :vereinfacht_club_id, :text
+    end
+  end
+
+  def down do
+    alter table(:settings) do
+      remove :vereinfacht_club_id
+      remove :vereinfacht_api_key
+      remove :vereinfacht_api_url
+    end
+  end
+end
diff --git a/priv/repo/migrations/20260218190000_add_vereinfacht_app_url.exs b/priv/repo/migrations/20260218190000_add_vereinfacht_app_url.exs
new file mode 100644
index 0000000..f10728c
--- /dev/null
+++ b/priv/repo/migrations/20260218190000_add_vereinfacht_app_url.exs
@@ -0,0 +1,15 @@
+defmodule Mv.Repo.Migrations.AddVereinfachtAppUrl do
+  use Ecto.Migration
+
+  def up do
+    alter table(:settings) do
+      add :vereinfacht_app_url, :text
+    end
+  end
+
+  def down do
+    alter table(:settings) do
+      remove :vereinfacht_app_url
+    end
+  end
+end
diff --git a/priv/resource_snapshots/repo/members/20260218185510.json b/priv/resource_snapshots/repo/members/20260218185510.json
new file mode 100644
index 0000000..ebfd40d
--- /dev/null
+++ b/priv/resource_snapshots/repo/members/20260218185510.json
@@ -0,0 +1,234 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"uuid_generate_v7()\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": true,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "first_name",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "last_name",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "email",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "join_date",
+      "type": "date"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "exit_date",
+      "type": "date"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "notes",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "city",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "street",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "house_number",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "postal_code",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "search_vector",
+      "type": "tsvector"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "membership_fee_start_date",
+      "type": "date"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "vereinfacht_contact_id",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": {
+        "deferrable": false,
+        "destination_attribute": "id",
+        "destination_attribute_default": null,
+        "destination_attribute_generated": null,
+        "index?": false,
+        "match_type": null,
+        "match_with": null,
+        "multitenancy": {
+          "attribute": null,
+          "global": null,
+          "strategy": null
+        },
+        "name": "members_membership_fee_type_id_fkey",
+        "on_delete": null,
+        "on_update": null,
+        "primary_key?": true,
+        "schema": "public",
+        "table": "membership_fee_types"
+      },
+      "scale": null,
+      "size": null,
+      "source": "membership_fee_type_id",
+      "type": "uuid"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "create_table_options": null,
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "4DF7F20D4C8D91E229906D6ADF87A4B5EB410672799753012DE4F0F49B470A51",
+  "identities": [
+    {
+      "all_tenants?": false,
+      "base_filter": null,
+      "index_name": "members_unique_email_index",
+      "keys": [
+        {
+          "type": "atom",
+          "value": "email"
+        }
+      ],
+      "name": "unique_email",
+      "nils_distinct?": true,
+      "where": null
+    }
+  ],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.Mv.Repo",
+  "schema": null,
+  "table": "members"
+}
\ No newline at end of file
diff --git a/priv/resource_snapshots/repo/settings/20260218185541.json b/priv/resource_snapshots/repo/settings/20260218185541.json
new file mode 100644
index 0000000..4334f9a
--- /dev/null
+++ b/priv/resource_snapshots/repo/settings/20260218185541.json
@@ -0,0 +1,140 @@
+{
+  "attributes": [
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"gen_random_uuid()\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": true,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": false,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "club_name",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "member_field_visibility",
+      "type": "map"
+    },
+    {
+      "allow_nil?": false,
+      "default": "true",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "include_joining_cycle",
+      "type": "boolean"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "default_membership_fee_type_id",
+      "type": "uuid"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "vereinfacht_api_url",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "vereinfacht_api_key",
+      "type": "text"
+    },
+    {
+      "allow_nil?": true,
+      "default": "nil",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "vereinfacht_club_id",
+      "type": "text"
+    },
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"(now() AT TIME ZONE 'utc')\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "inserted_at",
+      "type": "utc_datetime_usec"
+    },
+    {
+      "allow_nil?": false,
+      "default": "fragment(\"(now() AT TIME ZONE 'utc')\")",
+      "generated?": false,
+      "precision": null,
+      "primary_key?": false,
+      "references": null,
+      "scale": null,
+      "size": null,
+      "source": "updated_at",
+      "type": "utc_datetime_usec"
+    }
+  ],
+  "base_filter": null,
+  "check_constraints": [],
+  "create_table_options": null,
+  "custom_indexes": [],
+  "custom_statements": [],
+  "has_create_action": true,
+  "hash": "1038A37F021DFC347E325042D613B0359FEB7DAFAE3286CBCEAA940A52B71217",
+  "identities": [],
+  "multitenancy": {
+    "attribute": null,
+    "global": null,
+    "strategy": null
+  },
+  "repo": "Elixir.Mv.Repo",
+  "schema": null,
+  "table": "settings"
+}
\ No newline at end of file
diff --git a/test/mv/config_vereinfacht_test.exs b/test/mv/config_vereinfacht_test.exs
new file mode 100644
index 0000000..d7a3360
--- /dev/null
+++ b/test/mv/config_vereinfacht_test.exs
@@ -0,0 +1,83 @@
+defmodule Mv.ConfigVereinfachtTest do
+  @moduledoc """
+  Tests for Mv.Config Vereinfacht-related helpers.
+  """
+  use Mv.DataCase, async: false
+
+  describe "vereinfacht_env_configured?/0" do
+    test "returns false when no Vereinfacht ENV variables are set" do
+      clear_vereinfacht_env()
+      refute Mv.Config.vereinfacht_env_configured?()
+    end
+
+    test "returns true when VEREINFACHT_API_URL is set" do
+      set_vereinfacht_env("VEREINFACHT_API_URL", "https://api.example.com")
+      assert Mv.Config.vereinfacht_env_configured?()
+    after
+      clear_vereinfacht_env()
+    end
+
+    test "returns true when VEREINFACHT_CLUB_ID is set" do
+      set_vereinfacht_env("VEREINFACHT_CLUB_ID", "2")
+      assert Mv.Config.vereinfacht_env_configured?()
+    after
+      clear_vereinfacht_env()
+    end
+  end
+
+  describe "vereinfacht_configured?/0" do
+    test "returns false when no config is set" do
+      clear_vereinfacht_env()
+      # Settings may have nil for vereinfacht fields
+      refute Mv.Config.vereinfacht_configured?()
+    end
+  end
+
+  describe "vereinfacht_contact_view_url/1" do
+    test "returns nil when API URL is not configured" do
+      clear_vereinfacht_env()
+      assert Mv.Config.vereinfacht_contact_view_url("123") == nil
+    end
+
+    test "returns app contact view URL when API URL is set (derived app URL)" do
+      clear_vereinfacht_env()
+      clear_vereinfacht_app_url_from_settings()
+      set_vereinfacht_env("VEREINFACHT_API_URL", "https://api.example.com/api/v1")
+
+      assert Mv.Config.vereinfacht_contact_view_url("42") ==
+               "https://app.example.com/en/admin/finances/contacts/42"
+    after
+      clear_vereinfacht_env()
+    end
+
+    test "returns app contact view URL when VEREINFACHT_APP_URL is set" do
+      set_vereinfacht_env("VEREINFACHT_APP_URL", "https://app.verein.visuel.dev")
+
+      assert Mv.Config.vereinfacht_contact_view_url("abc") ==
+               "https://app.verein.visuel.dev/en/admin/finances/contacts/abc"
+    after
+      clear_vereinfacht_env()
+    end
+  end
+
+  defp set_vereinfacht_env(key, value) do
+    System.put_env(key, value)
+  end
+
+  defp clear_vereinfacht_env do
+    System.delete_env("VEREINFACHT_API_URL")
+    System.delete_env("VEREINFACHT_API_KEY")
+    System.delete_env("VEREINFACHT_CLUB_ID")
+    System.delete_env("VEREINFACHT_APP_URL")
+  end
+
+  defp clear_vereinfacht_app_url_from_settings do
+    case Mv.Membership.get_settings() do
+      {:ok, settings} ->
+        Mv.Membership.update_settings(settings, %{vereinfacht_app_url: nil})
+
+      _ ->
+        :ok
+    end
+  end
+end
diff --git a/test/mv/vereinfacht/changes/sync_contact_test.exs b/test/mv/vereinfacht/changes/sync_contact_test.exs
new file mode 100644
index 0000000..aa102a5
--- /dev/null
+++ b/test/mv/vereinfacht/changes/sync_contact_test.exs
@@ -0,0 +1,92 @@
+defmodule Mv.Vereinfacht.Changes.SyncContactTest do
+  @moduledoc """
+  Tests for Mv.Vereinfacht.Changes.SyncContact.
+
+  When Vereinfacht is not configured, member create/update should succeed
+  and vereinfacht_contact_id remains nil.
+  """
+  use Mv.DataCase, async: false
+
+  alias Mv.Membership
+
+  setup do
+    clear_vereinfacht_env()
+    :ok
+  end
+
+  describe "member create when Vereinfacht not configured" do
+    test "member is created and vereinfacht_contact_id is nil" do
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+
+      attrs = %{
+        first_name: "Sync",
+        last_name: "Test",
+        email: "sync_test_#{System.unique_integer([:positive])}@example.com"
+      }
+
+      assert {:ok, member} = Membership.create_member(attrs, actor: system_actor)
+      assert member.vereinfacht_contact_id == nil
+    end
+  end
+
+  describe "member update when Vereinfacht not configured" do
+    test "member is updated and vereinfacht_contact_id is unchanged" do
+      member = Mv.Fixtures.member_fixture()
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+
+      assert {:ok, updated} =
+               Membership.update_member(member, %{first_name: "Updated"}, actor: system_actor)
+
+      assert updated.vereinfacht_contact_id == nil
+    end
+  end
+
+  describe "when Vereinfacht is configured" do
+    # Regression: after_transaction callback receives 2 args (changeset, result), not 3.
+    # If the callback had arity 3, create_member would raise BadArityError.
+    # Also: Client must send JSON-encoded body (iodata); raw map causes ArgumentError
+    # when the request is sent. With an unreachable URL we get :econnrefused before
+    # that, so this test would not catch the iodata bug; a Bypass/stub server would.
+    test "create_member succeeds and after_transaction runs without error (API may fail)" do
+      set_vereinfacht_env()
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+
+      attrs = %{
+        first_name: "API",
+        last_name: "Test",
+        email: "api_test_#{System.unique_integer([:positive])}@example.com"
+      }
+
+      assert {:ok, member} = Membership.create_member(attrs, actor: system_actor)
+      assert member.id
+      # Sync may fail (e.g. connection refused), so contact_id can stay nil
+    after
+      clear_vereinfacht_env()
+    end
+
+    test "update_member succeeds and after_transaction runs without error (API may fail)" do
+      set_vereinfacht_env()
+      member = Mv.Fixtures.member_fixture()
+      system_actor = Mv.Helpers.SystemActor.get_system_actor()
+
+      assert {:ok, updated} =
+               Membership.update_member(member, %{first_name: "Updated"}, actor: system_actor)
+
+      assert updated.id == member.id
+    after
+      clear_vereinfacht_env()
+    end
+  end
+
+  defp set_vereinfacht_env do
+    System.put_env("VEREINFACHT_API_URL", "http://127.0.0.1:1/api/v1")
+    System.put_env("VEREINFACHT_API_KEY", "test-key")
+    System.put_env("VEREINFACHT_CLUB_ID", "2")
+  end
+
+  defp clear_vereinfacht_env do
+    System.delete_env("VEREINFACHT_API_URL")
+    System.delete_env("VEREINFACHT_API_KEY")
+    System.delete_env("VEREINFACHT_CLUB_ID")
+  end
+end
diff --git a/test/mv/vereinfacht/client_test.exs b/test/mv/vereinfacht/client_test.exs
new file mode 100644
index 0000000..d936adc
--- /dev/null
+++ b/test/mv/vereinfacht/client_test.exs
@@ -0,0 +1,50 @@
+defmodule Mv.Vereinfacht.ClientTest do
+  @moduledoc """
+  Tests for Mv.Vereinfacht.Client.
+
+  Only tests the "not configured" path; no real HTTP calls. Config reads from
+  ENV first, then from Settings (DB), so we use DataCase so get_settings() is available.
+  """
+  use Mv.DataCase, async: false
+
+  alias Mv.Vereinfacht.Client
+
+  setup do
+    clear_vereinfacht_env()
+    :ok
+  end
+
+  describe "create_contact/1" do
+    test "returns {:error, :not_configured} when Vereinfacht is not configured" do
+      member = build_member_struct()
+
+      assert Client.create_contact(member) == {:error, :not_configured}
+    end
+  end
+
+  describe "update_contact/2" do
+    test "returns {:error, :not_configured} when Vereinfacht is not configured" do
+      member = build_member_struct()
+
+      assert Client.update_contact("123", member) == {:error, :not_configured}
+    end
+  end
+
+  defp build_member_struct do
+    %{
+      first_name: "Test",
+      last_name: "User",
+      email: "test@example.com",
+      street: "Street 1",
+      house_number: "2",
+      postal_code: "12345",
+      city: "Berlin"
+    }
+  end
+
+  defp clear_vereinfacht_env do
+    System.delete_env("VEREINFACHT_API_URL")
+    System.delete_env("VEREINFACHT_API_KEY")
+    System.delete_env("VEREINFACHT_CLUB_ID")
+  end
+end
diff --git a/test/mv/vereinfacht/vereinfacht_test.exs b/test/mv/vereinfacht/vereinfacht_test.exs
new file mode 100644
index 0000000..08f73b9
--- /dev/null
+++ b/test/mv/vereinfacht/vereinfacht_test.exs
@@ -0,0 +1,59 @@
+defmodule Mv.VereinfachtTest do
+  @moduledoc """
+  Tests for Mv.Vereinfacht business logic.
+
+  No real API calls; tests "not configured" path and pure helpers (format_error).
+  """
+  use Mv.DataCase, async: false
+
+  alias Mv.Vereinfacht
+
+  setup do
+    clear_vereinfacht_env()
+    :ok
+  end
+
+  describe "sync_member/1" do
+    test "returns :ok when Vereinfacht is not configured (no-op)" do
+      member = Mv.Fixtures.member_fixture()
+
+      assert Vereinfacht.sync_member(member) == :ok
+    end
+  end
+
+  describe "sync_members_without_contact/0" do
+    test "returns {:error, :not_configured} when Vereinfacht is not configured" do
+      assert Vereinfacht.sync_members_without_contact() == {:error, :not_configured}
+    end
+  end
+
+  describe "format_error/1" do
+    test "formats HTTP error with detail" do
+      assert Vereinfacht.format_error({:http, 422, "The email field is required."}) ==
+               "Vereinfacht: The email field is required."
+    end
+
+    test "formats HTTP error without detail" do
+      assert Vereinfacht.format_error({:http, 500, nil}) ==
+               "Vereinfacht: API error (HTTP 500)."
+    end
+
+    test "formats request_failed" do
+      assert Vereinfacht.format_error({:request_failed, %{reason: :econnrefused}}) ==
+               "Vereinfacht: Request failed (e.g. connection error)."
+    end
+
+    test "formats invalid_response and other terms" do
+      assert Vereinfacht.format_error({:invalid_response, %{}}) ==
+               "Vereinfacht: Invalid API response."
+
+      assert Vereinfacht.format_error(:timeout) == "Vereinfacht: :timeout"
+    end
+  end
+
+  defp clear_vereinfacht_env do
+    System.delete_env("VEREINFACHT_API_URL")
+    System.delete_env("VEREINFACHT_API_KEY")
+    System.delete_env("VEREINFACHT_CLUB_ID")
+  end
+end
diff --git a/test/mv/vereinfacht/vereinfacht_test_README.md b/test/mv/vereinfacht/vereinfacht_test_README.md
new file mode 100644
index 0000000..993af47
--- /dev/null
+++ b/test/mv/vereinfacht/vereinfacht_test_README.md
@@ -0,0 +1,29 @@
+# Vereinfacht tests – scope and rationale
+
+## Constraint: no real API in CI
+
+Tests do **not** call the real Vereinfacht API or a shared test endpoint. All tests use dummy data and either:
+
+- Assert behaviour when **Vereinfacht is not configured** (ENV + Settings unset), or  
+- Run the **full Member/User flow** with a **unreachable URL** (e.g. `http://127.0.0.1:1`) so the HTTP client fails fast (e.g. `:econnrefused`) and we only assert that the application path does not crash.
+
+## What the tests cover
+
+| Test file | What it tests | Why it’s enough without an API |
+|-----------|----------------|---------------------------------|
+| **ConfigVereinfachtTest** | `vereinfacht_env_configured?`, `vereinfacht_configured?`, `vereinfacht_contact_view_url` with ENV set/cleared | Pure config logic; no HTTP. |
+| **ClientTest** | `create_contact/1` and `update_contact/2` return `{:error, :not_configured}` when nothing is configured | Ensures the client does not call Req when config is missing. |
+| **VereinfachtTest** | `sync_members_without_contact/0` returns `{:error, :not_configured}` when not configured | Ensures bulk sync is a no-op when config is missing. |
+| **SyncContactTest** | Member create/update with SyncContact change: not configured → no sync; configured with bad URL → action still succeeds, sync may fail | Ensures the Ash change and after_transaction arity are correct and the action result is not broken by sync failures. |
+
+## What is *not* tested (and would need a stub or real endpoint)
+
+- Actual HTTP request shape (body, headers) and response handling (201/200, error codes).  
+- Persistence of `vereinfacht_contact_id` after a successful create.  
+- Translation of specific API error payloads into user messages.
+
+Those would require either a **Bypass** (or similar) stub in front of Req or a dedicated test endpoint; both are out of scope for the current “no real API” setup.
+
+## Conclusion
+
+Given the constraint that the API is not called in CI, the tests are **meaningful**: they cover config, “not configured” paths, and integration of SyncContact with Member create/update without crashing. They are **sufficient** for regression safety and refactoring; extending them with a Bypass stub would be an optional next step if we want to assert on request/response shape without hitting the real API.
diff --git a/test/mv_web/live/global_settings_live_config_test.exs b/test/mv_web/live/global_settings_live_config_test.exs
index 9ac75fd..106a020 100644
--- a/test/mv_web/live/global_settings_live_config_test.exs
+++ b/test/mv_web/live/global_settings_live_config_test.exs
@@ -71,4 +71,18 @@ defmodule MvWeb.GlobalSettingsLiveConfigTest do
       end
     end
   end
+
+  describe "Vereinfacht Integration section" do
+    setup %{conn: conn} do
+      admin_user = Mv.Fixtures.user_with_role_fixture("admin")
+      conn = MvWeb.ConnCase.conn_with_password_user(conn, admin_user)
+      {:ok, conn: conn}
+    end
+
+    @tag :ui
+    test "settings page shows Vereinfacht Integration section", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/settings")
+      assert html =~ "Vereinfacht"
+    end
+  end
 end
diff --git a/test/test_helper.exs b/test/test_helper.exs
index c6cb1b8..01a0613 100644
--- a/test/test_helper.exs
+++ b/test/test_helper.exs
@@ -1,3 +1,9 @@
+# Ensure tests never hit the real Vereinfacht API (e.g. when .env is loaded by just).
+# Tests that need "configured" sync set a fake URL (127.0.0.1:1) in their own setup.
+System.delete_env("VEREINFACHT_API_URL")
+System.delete_env("VEREINFACHT_API_KEY")
+System.delete_env("VEREINFACHT_CLUB_ID")
+
 ExUnit.start(
   # shows 10 slowest tests at the end of the test run
   # slowest: 10