There was an error when an email was already used

apps/registration/forms.py

@@ -22,6 +22,15 @@ class SignupForm(UserCreationForm):
         ],
     )
 
+    def clean_email(self):
+        """
+        Ensure that the email address is unique.
+        """
+        email = self.data["email"]
+        if User.objects.filter(email=email).exists():
+            self.add_error("email", _("This email address is already used."))
+        return email
+
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.fields["first_name"].required = True