Did you create your account on your mobile?
I suspect the account was created through a shortcut login method (Google account or Apple account shortcut login) and doesn't yet have its own login email/password yet.
There are also other shortcut logins through Facebook and Steam.
Also, you have gravebumped a more than three year old thread.
NONE of the other posters on this thread had the same problem as yours.
I know the thread title sounded appropriate but, really, it's best to start your own thread.
Please, if you have more questions, start a new thread and we can get this one shut down.