set the first address as the main address as defualt

backend/account/views.py

@@ -142,7 +142,9 @@ class CreateAddressView(generics.CreateAPIView):
     permission_classes = [permissions.IsAuthenticated]
 
     def perform_create(self, serializer):
-        serializer.save(user=self.request.user)
+        user = self.request.user
+        is_first_address = not UserAddressModel.objects.filter(user=user).exists()
+        serializer.save(user=user, is_main=is_first_address)
 
 class EditAddressView(generics.UpdateAPIView):
     queryset = UserAddressModel.objects.all()