Whenever I try to post to the forum from my iPhone, it prompts me to set up my account. I was already logged in, but I tried inputting my username, email, and password anyways. It gave the error that the username was already selected.
I then tried logging out of my account in the app and logging back in and trying to post in the forum again, but it had the same problem.
I think it's something gone wrong with your new trial ability to study without an account.