diff --git a/lib/membership/member.ex b/lib/membership/member.ex
index 074f7e4..3af514e 100644
--- a/lib/membership/member.ex
+++ b/lib/membership/member.ex
@@ -500,50 +500,54 @@ defmodule Mv.Membership.Member do
       end
     end
 
-    # Validate required custom fields (actor from validation context only; no fallback)
+    # Validate required custom fields (actor from validation context only; no fallback).
+    # Only for create_member/update_member; skip for set_vereinfacht_contact_id (internal sync
+    # only sets vereinfacht_contact_id; custom fields were already validated and saved).
     validate fn changeset, context ->
-      provided_values = provided_custom_field_values(changeset)
-      actor = context.actor
+               provided_values = provided_custom_field_values(changeset)
+               actor = context.actor
 
-      case Mv.Membership.list_required_custom_fields(actor: actor) do
-        {:ok, required_custom_fields} ->
-          missing_fields = missing_required_fields(required_custom_fields, provided_values)
+               case Mv.Membership.list_required_custom_fields(actor: actor) do
+                 {:ok, required_custom_fields} ->
+                   missing_fields =
+                     missing_required_fields(required_custom_fields, provided_values)
 
-          if Enum.empty?(missing_fields) do
-            :ok
-          else
-            build_custom_field_validation_error(missing_fields)
-          end
+                   if Enum.empty?(missing_fields) do
+                     :ok
+                   else
+                     build_custom_field_validation_error(missing_fields)
+                   end
 
-        {:error, %Ash.Error.Forbidden{}} ->
-          Logger.warning(
-            "Required custom fields validation: actor not authorized to read CustomField"
-          )
+                 {:error, %Ash.Error.Forbidden{}} ->
+                   Logger.warning(
+                     "Required custom fields validation: actor not authorized to read CustomField"
+                   )
 
-          {:error,
-           field: :custom_field_values,
-           message:
-             "You are not authorized to perform this action. Please sign in again or contact support."}
+                   {:error,
+                    field: :custom_field_values,
+                    message:
+                      "You are not authorized to perform this action. Please sign in again or contact support."}
 
-        {:error, :missing_actor} ->
-          Logger.warning("Required custom fields validation: no actor in context")
+                 {:error, :missing_actor} ->
+                   Logger.warning("Required custom fields validation: no actor in context")
 
-          {:error,
-           field: :custom_field_values,
-           message:
-             "You are not authorized to perform this action. Please sign in again or contact support."}
+                   {:error,
+                    field: :custom_field_values,
+                    message:
+                      "You are not authorized to perform this action. Please sign in again or contact support."}
 
-        {:error, error} ->
-          Logger.error(
-            "Failed to load custom fields for validation: #{inspect(error)}. Required field validation cannot be performed."
-          )
+                 {:error, error} ->
+                   Logger.error(
+                     "Failed to load custom fields for validation: #{inspect(error)}. Required field validation cannot be performed."
+                   )
 
-          {:error,
-           field: :custom_field_values,
-           message:
-             "Unable to validate required custom fields. Please try again or contact support."}
-      end
-    end
+                   {:error,
+                    field: :custom_field_values,
+                    message:
+                      "Unable to validate required custom fields. Please try again or contact support."}
+               end
+             end,
+             where: [action_is([:create_member, :update_member])]
 
     # Validate member fields that are marked as required in settings or by Vereinfacht.
     # When settings cannot be loaded, we still enforce email + Vereinfacht-required fields.