Our app was rejected because it allowed users to enter promo codes to get a discounted version of our subscriptions. Both the original and the discounted products were published through the iTunes Store and paid through the IAP but we were told that the app contravened section 3.1.1 of their guidelines.
Now we are stuck and we wonder how apps like Deliveroo work: does anybody have a clue on how such functionality can be implemented and approved through the Apple review process?