[Fixed]-Test Django REST Framework Login Protected API using Postman?

You can use Basic Auth in POSTMAN. Refer to this screenshot:

You could change the HTTP Methods, URLs, Data Payload(under Body tab) etc in the POSTMAN console

UPDATE-1

After your comments, I tried to recreated the problem.What I did was:

1. created a view

    from rest_framework.views import APIView
    from rest_framework.permissions import IsAuthenticated
    from rest_framework.response import Response
   
    class MySampleView(APIView):
        permission_classes = (IsAuthenticated,)
   
        def get(self, request):
            return Response(data={"status": True})
   

2. Added to urls.py

    urlpatterns = [
        url(r'^mysampleview/$', MySampleView.as_view())
    ]
   

And my POSTMAN response are below:

Authorization Screenshot

Header Screenshot

My conclusion

You may enter wrong credentials, or something else. I would suggest you open a new POSTMAN tab and repeat the procedure, also try to login Django admin using the same credential which is already used in POSTMAN.