I am helping a friend with an app project, and nobody seems to know where AppID and AppSecret for Facebook came from. I.e. design studio didn't give access to Facebook dev account.
Is it safe to use a new AppID from a new Facebook dev account, given there are some users we wouldn't want to lose? I.e. will those previously registered users be able to log in again?
A user's Facebook sign-in ID are tied to a combination of their sign-in credentials and the application they sign in to. If you change the app ID in the Firebase project, the same person will get a new Facebook sign-in ID, and a new Firebase Authentication UID. So they will they have to sign in again indeed, and they will be a new user on the Firebase side.