StoreKit in-app purchases: lessons learned
1. When using sandbox user account, do not sign in using Preferences, just sign out and sign in when your app asks so.
2. Transaction receipt should be Base64 encoded before sending to Apple verification service. This is not mentioned in the docs.
3. Subscriptions should not be restored using restore API. Do not even try: Apple suggests sending relevant data from your application server.
4. Title/description you set in iTunes connect do not really matter if you supply products from the server. Only product id and the price tier matter. Everything else you supply by yourself.
5. Do not forget to sort the products elsewhere since it is impossible to sort them on iTunes Connect site.
6. Transaction receipt should be verified at apple server for two reasons: 1) secure validation; 2) this is the only way to get transaction details