[Fixed]-DjangoRestFramework serializer does not recognize 'username' attribute even though it exists

The issue is in your get_object method, you’re returning a 404 response instead of raising a Http404 exception. Because of that, the Response is being passed into your serializer, and clearly the Response does not have a username field.

The last part of your stack trace said

Original exception text was: ‘Response’ object has no attribute ‘username’.

Which was the signal: there is only one place where you are returning a Response back to a serializer.