diff --git a/api/custom_auth/serializers.py b/api/custom_auth/serializers.py
index 41ffe1e4e1f0..37cfeffaedba 100644
--- a/api/custom_auth/serializers.py
+++ b/api/custom_auth/serializers.py
@@ -1,8 +1,10 @@
 from django.conf import settings
+from djoser.conf import settings as djoser_settings
 from djoser.serializers import UserCreateSerializer, UserDeleteSerializer
 from rest_framework import serializers
 from rest_framework.authtoken.models import Token
 from rest_framework.exceptions import PermissionDenied
+from rest_framework.validators import UniqueValidator
 
 from organisations.invites.models import Invite
 from users.constants import DEFAULT_DELETE_ORPHAN_ORGANISATIONS_VALUE
@@ -18,17 +20,27 @@ class Meta:
 
 
 class CustomUserCreateSerializer(UserCreateSerializer):
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self.fields["key"] = serializers.SerializerMethodField()
+    key = serializers.SerializerMethodField()
 
     class Meta(UserCreateSerializer.Meta):
         fields = UserCreateSerializer.Meta.fields + (
             "is_active",
             "marketing_consent_given",
+            "key",
         )
         read_only_fields = ("is_active",)
         write_only_fields = ("sign_up_type",)
+        extra_kwargs = {
+            "email": {
+                "validators": [
+                    UniqueValidator(
+                        queryset=FFAdminUser.objects.all(),
+                        lookup="iexact",
+                        message=djoser_settings.CONSTANTS.messages.CANNOT_CREATE_USER_ERROR,
+                    )
+                ]
+            }
+        }
 
     def validate(self, attrs):
         attrs = super().validate(attrs)
@@ -42,8 +54,6 @@ def validate(self, attrs):
                 self.context.get("request"), email=email, raise_exception=True
             )
 
-        if FFAdminUser.objects.filter(email__iexact=email).count() != 0:
-            raise serializers.ValidationError({"detail": "Unable to create account"})
         attrs["email"] = email.lower()
         return attrs
 
diff --git a/api/custom_auth/tests/test_serializer.py b/api/custom_auth/tests/test_serializer.py
index baa4ad816fc3..ea13be6bafce 100644
--- a/api/custom_auth/tests/test_serializer.py
+++ b/api/custom_auth/tests/test_serializer.py
@@ -25,7 +25,7 @@ def test_CustomUserCreateSerializer_does_case_insensitive_lookup_with_email(db):
 
     # When
     assert serializer.is_valid() is False
-    assert serializer.errors["detail"][0].title() == "Unable To Create Account"
+    assert serializer.errors["email"][0].title() == "Unable To Create Account."
 
 
 def test_CustomUserCreateSerializer_calls_is_authentication_method_valid_correctly_if_auth_controller_is_installed(