I downloaded the app.
I've tried to sign up using different email address, and different passwords.
The "sign up for free" button changes from blue to orange and back to blue. I receive no other acknowledgement of action, no other notification.
Once or twice it said I had no internet connection. However I did.
Have no other problem with any other app or web page.
Looks like Pro Writing Aid doesn't want me.
Spent an hour on it. Moving on...