diff --git a/lib/membership/member.ex b/lib/membership/member.ex
index 73820f6..286bb1a 100644
--- a/lib/membership/member.ex
+++ b/lib/membership/member.ex
@@ -354,7 +354,15 @@ defmodule Mv.Membership.Member do
           Enum.reduce(custom_field_values_arg, %{}, fn cfv, acc ->
             custom_field_id = Map.get(cfv, "custom_field_id")
             value_map = Map.get(cfv, "value", %{})
-            actual_value = Map.get(value_map, "value")
+
+            # Support both "value" and "_union_value" keys, without using || to preserve false values
+            actual_value =
+              cond do
+                Map.has_key?(value_map, "value") -> Map.get(value_map, "value")
+                Map.has_key?(value_map, "_union_value") -> Map.get(value_map, "_union_value")
+                true -> nil
+              end
+
             Map.put(acc, custom_field_id, actual_value)
           end)
         end
diff --git a/test/membership/member_required_custom_fields_test.exs b/test/membership/member_required_custom_fields_test.exs
index 7467152..747cebd 100644
--- a/test/membership/member_required_custom_fields_test.exs
+++ b/test/membership/member_required_custom_fields_test.exs
@@ -69,6 +69,33 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
     }
   end
 
+  # Helper function to create all required custom fields with valid default values
+  defp all_required_custom_fields_with_defaults(%{
+         required_string_field: string_field,
+         required_integer_field: integer_field,
+         required_boolean_field: boolean_field,
+         required_date_field: date_field
+       }) do
+    [
+      %{
+        "custom_field_id" => string_field.id,
+        "value" => %{"_union_type" => "string", "_union_value" => "default"}
+      },
+      %{
+        "custom_field_id" => integer_field.id,
+        "value" => %{"_union_type" => "integer", "_union_value" => 0}
+      },
+      %{
+        "custom_field_id" => boolean_field.id,
+        "value" => %{"_union_type" => "boolean", "_union_value" => false}
+      },
+      %{
+        "custom_field_id" => date_field.id,
+        "value" => %{"_union_type" => "date", "_union_value" => ~D[2020-01-01]}
+      }
+    ]
+  end
+
   describe "create_member with required custom fields" do
     @valid_attrs %{
       first_name: "John",
@@ -84,15 +111,20 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "fails when required string custom field has nil value", %{
-      required_string_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => nil}
-        }
-      ]
+    test "fails when required string custom field has nil value",
+         %{
+           required_string_field: field
+         } = context do
+      # Start with all required fields having valid values
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "string", "_union_value" => nil}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -101,15 +133,20 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "fails when required string custom field has empty string value", %{
-      required_string_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => ""}
-        }
-      ]
+    test "fails when required string custom field has empty string value",
+         %{
+           required_string_field: field
+         } = context do
+      # Start with all required fields having valid values
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "string", "_union_value" => ""}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -118,15 +155,20 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "fails when required string custom field has whitespace-only value", %{
-      required_string_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "   "}
-        }
-      ]
+    test "fails when required string custom field has whitespace-only value",
+         %{
+           required_string_field: field
+         } = context do
+      # Start with all required fields having valid values
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "string", "_union_value" => "   "}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -135,30 +177,39 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "succeeds when required string custom field has valid value", %{
-      required_string_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "test value"}
-        }
-      ]
+    test "succeeds when required string custom field has valid value",
+         %{
+           required_string_field: field
+         } = context do
+      # Start with all required fields having valid values, then update the string field
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "string", "_union_value" => "test value"}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "fails when required integer custom field has nil value", %{
-      required_integer_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "integer", "value" => nil}
-        }
-      ]
+    test "fails when required integer custom field has nil value",
+         %{
+           required_integer_field: field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "integer", "_union_value" => nil}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -167,45 +218,49 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "succeeds when required integer custom field has zero value", %{
-      required_integer_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "integer", "value" => 0}
-        }
-      ]
+    test "succeeds when required integer custom field has zero value",
+         %{
+           required_integer_field: _field
+         } = context do
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "succeeds when required integer custom field has positive value", %{
-      required_integer_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "integer", "value" => 42}
-        }
-      ]
+    test "succeeds when required integer custom field has positive value",
+         %{
+           required_integer_field: field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "integer", "_union_value" => 42}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "fails when required boolean custom field has nil value", %{
-      required_boolean_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "boolean", "value" => nil}
-        }
-      ]
+    test "fails when required boolean custom field has nil value",
+         %{
+           required_boolean_field: field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "boolean", "_union_value" => nil}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -214,45 +269,49 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "succeeds when required boolean custom field has false value", %{
-      required_boolean_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "boolean", "value" => false}
-        }
-      ]
+    test "succeeds when required boolean custom field has false value",
+         %{
+           required_boolean_field: _field
+         } = context do
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "succeeds when required boolean custom field has true value", %{
-      required_boolean_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "boolean", "value" => true}
-        }
-      ]
+    test "succeeds when required boolean custom field has true value",
+         %{
+           required_boolean_field: field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "boolean", "_union_value" => true}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "fails when required date custom field has nil value", %{
-      required_date_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "date", "value" => nil}
-        }
-      ]
+    test "fails when required date custom field has nil value",
+         %{
+           required_date_field: field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "date", "_union_value" => nil}}
+          else
+            cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -261,57 +320,60 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "succeeds when required date custom field has valid date value", %{
-      required_date_field: field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "date", "value" => ~D[2020-01-01]}
-        }
-      ]
+    test "succeeds when required date custom field has valid date value",
+         %{
+           required_date_field: _field
+         } = context do
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "succeeds when multiple required custom fields are provided", %{
-      required_string_field: string_field,
-      required_integer_field: integer_field,
-      required_boolean_field: boolean_field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => string_field.id,
-          "value" => %{"type" => "string", "value" => "test"}
-        },
-        %{
-          "custom_field_id" => integer_field.id,
-          "value" => %{"type" => "integer", "value" => 42}
-        },
-        %{
-          "custom_field_id" => boolean_field.id,
-          "value" => %{"type" => "boolean", "value" => true}
-        }
-      ]
+    test "succeeds when multiple required custom fields are provided",
+         %{
+           required_string_field: string_field,
+           required_integer_field: integer_field,
+           required_boolean_field: boolean_field
+         } = context do
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          cond do
+            cfv["custom_field_id"] == string_field.id ->
+              %{cfv | "value" => %{"_union_type" => "string", "_union_value" => "test"}}
+
+            cfv["custom_field_id"] == integer_field.id ->
+              %{cfv | "value" => %{"_union_type" => "integer", "_union_value" => 42}}
+
+            cfv["custom_field_id"] == boolean_field.id ->
+              %{cfv | "value" => %{"_union_type" => "boolean", "_union_value" => true}}
+
+            true ->
+              cfv
+          end
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "fails when one of multiple required custom fields is missing", %{
-      required_string_field: string_field,
-      required_integer_field: integer_field
-    } do
-      custom_field_values = [
-        %{
-          "custom_field_id" => string_field.id,
-          "value" => %{"type" => "string", "value" => "test"}
-        }
-        # Missing required_integer_field
-      ]
+    test "fails when one of multiple required custom fields is missing",
+         %{
+           required_string_field: string_field,
+           required_integer_field: integer_field
+         } = context do
+      # Provide only string field, missing integer, boolean, and date
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.filter(fn cfv ->
+          cfv["custom_field_id"] == string_field.id
+        end)
+        |> Enum.map(fn cfv ->
+          %{cfv | "value" => %{"_union_type" => "string", "_union_value" => "test"}}
+        end)
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -320,19 +382,26 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ integer_field.name
     end
 
-    test "succeeds when optional custom field is missing", %{optional_field: field} do
-      attrs = Map.put(@valid_attrs, :custom_field_values, [])
+    test "succeeds when optional custom field is missing", %{} = context do
+      # Provide all required fields, but no optional field
+      custom_field_values = all_required_custom_fields_with_defaults(context)
+
+      attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
       assert {:ok, _member} = Membership.create_member(attrs)
     end
 
-    test "succeeds when optional custom field has nil value", %{optional_field: field} do
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => nil}
-        }
-      ]
+    test "succeeds when optional custom field has nil value",
+         %{optional_field: field} = context do
+      # Provide all required fields plus optional field with nil
+      custom_field_values =
+        all_required_custom_fields_with_defaults(context) ++
+          [
+            %{
+              "custom_field_id" => field.id,
+              "value" => %{"_union_type" => "string", "_union_value" => nil}
+            }
+          ]
 
       attrs = Map.put(@valid_attrs, :custom_field_values, custom_field_values)
 
@@ -341,16 +410,12 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
   end
 
   describe "update_member with required custom fields" do
-    test "fails when removing a required custom field value", %{
-      required_string_field: field
-    } do
-      # Create member with required custom field
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "test"}
-        }
-      ]
+    test "fails when removing a required custom field value",
+         %{
+           required_string_field: field
+         } = context do
+      # Create member with all required custom fields
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       {:ok, member} =
         Membership.create_member(%{
@@ -368,16 +433,12 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "fails when setting required custom field value to empty", %{
-      required_string_field: field
-    } do
-      # Create member with required custom field
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "test"}
-        }
-      ]
+    test "fails when setting required custom field value to empty",
+         %{
+           required_string_field: field
+         } = context do
+      # Create member with all required custom fields
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       {:ok, member} =
         Membership.create_member(%{
@@ -387,13 +448,16 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
           custom_field_values: custom_field_values
         })
 
-      # Try to update with empty value
-      updated_custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => ""}
-        }
-      ]
+      # Try to update with empty value for the string field
+      updated_custom_field_values =
+        all_required_custom_fields_with_defaults(context)
+        |> Enum.map(fn cfv ->
+          if cfv["custom_field_id"] == field.id do
+            %{cfv | "value" => %{"_union_type" => "string", "_union_value" => ""}}
+          else
+            cfv
+          end
+        end)
 
       assert {:error, %Ash.Error.Invalid{errors: errors}} =
                Membership.update_member(member, %{
@@ -404,16 +468,12 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
       assert error_message(errors, :custom_field_values) =~ field.name
     end
 
-    test "succeeds when updating required custom field to valid value", %{
-      required_string_field: field
-    } do
-      # Create member with required custom field
-      custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "old value"}
-        }
-      ]
+    test "succeeds when updating required custom field to valid value",
+         %{
+           required_string_field: field
+         } = context do
+      # Create member with all required custom fields
+      custom_field_values = all_required_custom_fields_with_defaults(context)
 
       {:ok, member} =
         Membership.create_member(%{
@@ -423,13 +483,31 @@ defmodule Mv.Membership.MemberRequiredCustomFieldsTest do
           custom_field_values: custom_field_values
         })
 
-      # Update with new valid value
-      updated_custom_field_values = [
-        %{
-          "custom_field_id" => field.id,
-          "value" => %{"type" => "string", "value" => "new value"}
-        }
-      ]
+      # Load existing custom field values to get their IDs
+      {:ok, member_with_cfvs} = Ash.load(member, :custom_field_values)
+
+      # Update with new valid value for the string field, using existing IDs
+      updated_custom_field_values =
+        member_with_cfvs.custom_field_values
+        |> Enum.map(fn cfv ->
+          if cfv.custom_field_id == field.id do
+            %{
+              "id" => cfv.id,
+              "custom_field_id" => cfv.custom_field_id,
+              "value" => %{"_union_type" => "string", "_union_value" => "new value"}
+            }
+          else
+            # Keep other fields as they are
+            value_type = Atom.to_string(cfv.value.type)
+            actual_value = cfv.value.value
+
+            %{
+              "id" => cfv.id,
+              "custom_field_id" => cfv.custom_field_id,
+              "value" => %{"_union_type" => value_type, "_union_value" => actual_value}
+            }
+          end
+        end)
 
       assert {:ok, _updated_member} =
                Membership.update_member(member, %{