The only documentation I could find is https://developer.apple.com/documentation/storekit/in-app_purchase/original_api_for_in-app_purchase/subscriptions_and_offers/implementing_offer_codes_in_your_app is so half baked. docs which has absolutely ZERO code samples and ZERO example implementations linked to it.

Thanks for your answer Rich. I just want to say this is a pathetic development experience, but I expect nothing more from AppStore technical team. Can you kindly convey this to your tech team and ask them to allow us to test in Sandbox environment.

@DimpleAShah, Did it work for you? We're in the same situation and unable to move forward after user enters the Offer code.