How to implement in app purchases for mobile?

Is there a sample project that includes iap for iOS and Android? Will there be future Marketplace solutions for this? Unity already has a number of options in this regard, and it’s something almost all mobile developers need.

I am also looking for one since online selling nowadays is the game for most of the people. People check every website for a good products. Especially delta 8 (D8) products from area52.com site