There is a lot of information about IAP validation, but how do I validate app purchase?
Also I want to sell my app and use same Title ID as free app uses. But it can be submitted only one pair of Google App Package ID and key at add-on page.
I already made IAP validation in my free app that works fine.
Application licensing is managed by Google Play directly - when you purchase the app, you get a license for it, which is checked when you launch it and connect to Google's service. We will be adding a registration code system intended for PC games in a future update, so technically you could use that to enable an additional layer of licensing, if you're concerned about hackers side-loading your game.
In answer to the question on how to manage a free versus paid version of the same game, it depends upon how you're detecting that difference and managing it. You can use a single Title ID in our service for both, or you could use a Title ID for each and share data for the player via User Publisher Data (and User Publisher Read-Only Data, etc.). Since you can only submit this as one application in Google Play, with two different "modes", it would probably be best to manage it as a single Title ID in PlayFab, so that all the data is in one place. The difference in behavior is really on the client side, then.
