This is the extension that I created to use in our game. Does not support subscriptions right now.
I've integrated purchase verification in it, so gives some protection from frauded purchases. See more info about purchase verification here: https://developer.android.com/google/play/billing/billing_library_overview#Verify-purchase-device
Also in case of failures during purchase consuming this extension will automatically resend consume request. Even after game restart it will still try to resend requests.
See documentation here: https://docs.google.com/document/d/15VdGaniwRhevYtw_gcAqSMah_k7HsxdplPBHiWNnbe8/edit?usp=sharing
Also there is an advanced tutorial with code examples available at gmdevblog.com
With any questions write to firstname.lastname@example.org