i’ve been looking for any ways to introduce payment methods and microtransactions for my mobile game, yet i haven’t found any since 2011, no joke, is not something i’m in a hurry, but seriously, haven’t found any tutorial neither google nor youtube videos
the match three sample on the learn tab provides full source on how to do in app payments. I think there might be something on the wiki now too
There are numerous tutorials for iOS and Android payments around the internet. Ray Wenderlich has a bunch of good posts from various authors on the iOS side (https://www.raywenderlich.com/?s=in-app+purchase&cof=FORID%3A10). Of course the iOS (In-App Purchase - Apple Developer) or Android (Google Play's billing system overview) documentation on in-app purchase is a great place to start and they usually have several samples to walk through. Have you looked through any of this noted documentation?