We are currently implementing Subscriptions via the In App Purchase SDK.
We rely on the RTDN Notifications in our backend to manage purchases (we send the user id beforehand so we know with which user to attribute a purchase notification).
Is there an API our backend can call to fulfill the purchase itself? Or can it only be managed by our app (via notifyFulfillment()) ?
This model works perfectly for Google/Apple subscriptions, so we'd prefer to implement it the same way for Amazon IAP.