This should be a very simple and quick issue for the Android App log in.
After clicking “Sign in now”, we have three options
Sign in with Facebook
Sign in with Google and
Sign in with Email.
I think you should also offer Sign in with Username
It’s only when one resorts to email option that one sees Username given as the first option although email hint is in the box.
Yes I know it works, but it has always puzzled me why I have to resort to email only to find I could just put DW7 and password.
(And I’m doing it frequently in order to update or synchronise courses that I’ve amended on the web.)