On both Android and iOS, if a user buys a subscription and then tries to buy
it again, both the Google Play Store or Apple App Store will post a warning
that the user already owns the subscription.
For Amazon Fire, I am using the In-App Purchase ANE for Amazon, and because
you use the App Tester on a Fire device instead of talking directly to the
AppStore, it is a little confusing as to what will actually happen in
production. Debugging from my device using the App Tester on a Fire device,
I can purchase the subscription as often as I like without getting any
warning that I already own the subscription. Do I need to poll the user's
past purchases and and handle creating this warning myself, or will it
actually stop me from making a repeat subscription purchase in production???