Fix returning member pk instead of user pk

website/events/api/serializers.py

@@ -223,7 +223,7 @@ class RegistrationListSerializer(serializers.ModelSerializer):
 
     def _member(self, instance):
         if instance.member:
-            return instance.member.pk
+            return instance.member.user.pk
         return None
 
     def _name(self, instance):