Pre-saved App user when signing up, How?

I am trying to build a mobile app, it’s a rewards/discount mobile app exclusively for our customers. How can I create a “Sign up” page wherein only the assigned email or user name can create an account?

Thanks in advance!

Make the accounts in advance, so they are actually logging in, a custom password reset could make this a good user experience. This will need a high level of subscription to Adalo and 3rd party tool like Xano

I’ve also a solution listed at wenocodeshare