Panga12 Sorry, it's difficult to troubleshoot this without access to the website.
So, based on what you've said, it sounds like you have saved the shortcut, you were able to log in from your phone, and you got to the point where you can add a new device, enter a name, then you can't save?
If I were you, I'd try going to their website, which appears to be https://app.dev.umsatz.io, in Vanadium. Then tap the icon with lines with circles at the ends to the left of the address in the address bar. From there tap permissions, and try granting JavaScript JIT. You may also try enabling Ads. After doing that, go back to the shortcut you created and try adding a device and saving the name again.