I have a paid app published in Apple AppStore.
I want to encourage the buyers of the app by giving them some extra bunus.
Here I mean the purchasing the app itself, not In-App Purchases.
How can I verify that the client really bought the app?
I can ask the client to forward me an 'Order Number' of his purchase (receipt), but how can I verify this order number?
Is there any other ways to track the fact of purchasing the app?