Sign in with an Existing Account
If you have signed up for your Untappd account with Apple or already connected your account, click the “Sign in with Apple” button, authorize with Apple, and you will be taken to the Home page on untappd.com:
Sign in with an account that has not been linked
You will not be able to connect your Untappd account to Sign in with Apple from the web. Your account must already be connected or created on mobile before signing in via the web.
If your Apple account is not connected to an Untappd account, when you enter your login information, you will be redirected back out to the sign in page where you will see an error message that says, “Sign in with Apple currently only supports existing accounts, creating an account is not supported.”