I am in the process of migrating two separate free/paid apps to an In-App-Purchase based payment model. I have 4000 existing paid users, and so I would need a way to know if they already bought the old paid app, and if so they should have access to the same functionality that newer users who paid via the new in-app-purchase model do.
I could ask existing users to register something like their email, store that on some server and make it possible to use that to validate their purchase if they reinstall the app. But I would ideally want to make the transition seamless for existing users, so I'm wondering if there are any methods that don't require any user interaction?
I was thinking that maybe I can get some kind of UID that is tied to their Google account (they must have one since they bought the paid app on Google Play). Can I for example use Firebase to retrieve such a UID without having to ask the user to sign in? Looking at the guide for Authenticating users with Firebase and Flutter, it seems that it's necessary to call SignInWithGoogle()
to get a UID, which I assume prompts the user to sign in with their Google account and password?
I have considered using the device ID, but that is not really an option since the purchase of an app should be tied to a user and not a specific device which will eventually be replaced.
