As far as I'm aware, the app hasn't been updated in a very long time. It's well past its update on iOS, and I believe the game was just a test to see what they could make with a mobile app. It's very unlikely that the game will be revisited anytime soon.

I've got the full verion, and it's also not working

My boyfriend I have the same problem :(

Yeah. In 2017 I tried to log in and it worked. Then a few months later when they added # tags at the end of the usernames, it wouldn’t work. You’re not the only person experiencing this.

Unfortunately, it's unlikely that this bug will be fixed, due to the developer working on RFC leaving Atelier801 last year :(