Apple has many certificates to ensure security and authentication for their apps, and one of those certificates is the "Sign-in with Apple".
In some cases, it may not be enabled for your app. You will know it because Apple will send you an email with a subject similar to "Your app has misconfigured Sign-in with Apple", or "Your app is misconfigured".
Please take into account that your iOS bundle id is currently accessible via request to our Customer Service, but soon it will be available in the Settings section at Passion.io
Here is the video explaining how to solve the misconfigured Sign-in with Apple in just 3 minutes:
https://www.loom.com/share/864e8f8c10d44ed3a7ff2acfe1fd1de2