If you've never used our service before, you can create a new account and start browsing for books right away. You can create an account using your email address or login with either Facebook, Gmail or with Apple ID.
If you are an existing user: If you have logged in to the app for the first time with either Facebook, Gmail or Apple ID please log out of the app and log back in with your account’s email address and password as you have used in the past.
Log in with Apple ID: For some users, the Sign In With Apple has a built-in feature which allows the user to hide their email address and create a unique, random email address. If you have signed in with the “Hide my email” feature your account’s email address will be the unique email created by Apple. The email address will appear in your sign-up confirmation email.
We highly recommend to change the email address associated with the account please contact our support team Here
You can read more about “Hide my email” here