If you are planning to add IAPs to your game have a look at this module as an option to use if your needs are simple / use it as a supplement to existing examples and documentation on IAP.
There are no docs right now, just look at the example/source to see how it works. The main thing about it is if you use the same product ids for Google Play and Apple App Store it should just work.
This only has support for Google Play and Amazon App Store, but everything else could be added. Pull requests welcome!