If you previously signed up with Synctuition manually with your email and password and you now select the Apple login feature, a new private account will be created. When looking at your profile you will see a randomized email generated when you log in via your Apple account but hide your email from Synctuition.
If you log in this way and you do see this random email, and the account does not have any active subscriptions. Log out of this account and log in manually with your email and password.
If you are still having issues, please reach out to us through our contact page: https://synctuition.com/web/contact-us/