The RP Diet Coach app allows users to sign in via multiple methods.
We recommend that once you choose your method of log-in, that you sign in with that method every time. Otherwise, there is a risk of creating multiple accounts.
Note: Sign in with Apple is only available to iPhone users
You can choose to sign up and sign in using your existing Facebook or Google Accounts
Check out this article on setting up and signing in with Apple: Sign in with Apple