question

You need to enter your applications configuration info in the Add-ons->Google tab for your title. That configuration info lets us query Google on your behalf, to verify the receipt. We also track on receipt usage, to prevent replay attacks, as well as verifying the contents of the receipt to make sure it's actually a receipt for your game. Once we've done all that, we automatically find the item in the game catalog and add an instance to the player's inventory, so that the whole process is secure.