This is sorta what customers expect. When they want a refund or have a problem, they ask the developer. They don't understand the payments are all going through apple AND that apple is responsible for all billing support. There is no way to even look up a customer or get a list of your customers with IAP, aside from using something like RevenueCat that tries to link your user accounts with the device receipts to figure out who is subscribed. Customers find it ridiculous that you can't help them with any billing questions at all.