Unity IAP iOS app rejected

Your app offers a content subscription but does not have a mechanism in place to support the requirement that the subscription content be available to the user on all of their iOS devices.

Next Steps To resolve this issue, please modify your app to include an optional user registration feature to deliver subscription content to all of the user's iOS devices. Such user registration must be made optional, not required. We also recommend indicating that registering is required to access the subscription content from their other iOS devices - and providing a way to register later, if users wish to have access to this content at a future time.

This is the response I got from the Apple when I tried to publish my game. Any idea how to fix it ? I thought Unity's IAP already handles the login and all these things.

 

Do you have a non-renewing subscription? Doing a little research seems to imply that Apple is asking for a "login" or other user verification to be able to sync the subscription across devices, similar to a Restore button for non-consumables but implemented yourself. Asking for such information seems a bit contrary to recent GDPR requirements, so it may also be a temporary issue with Apples approval process. I would suggest that you open an appeal with Apple to get more information. I will check here too.