Callback for PurchasingManager.
Callback for PurchasingManager.initiateGetUserIdRequest()
Callback for initiatePurchaseUpdatesRequest(Offset).
Callback for initiatePurchaseUpdatesRequest(Offset).
"You must use this method to sync purchases made from other devices onto this device, and to sync revoked entitlements across all instances of your app."
Callback for PurchasingManager.
Callback for PurchasingManager.registerObserver(Activity)
This class registers itself as the observer for the com.amazon.inapp.purchasing.PurchasingManager upon construction.
Clients shall not use this class directly. Instead, use com.mle.android.iap.amazon.AmazonIapUtils.
TODO: Create rx observables that get new values when the callbacks are called. Futures are one-off and a bad match for this API.