Did you use the signature for your app from the Google developer console? It would be under Services & API's. You take that entire string and enter it in the CocoonJS compiler in In-App Purchases --> Configuration.
Then click the Extensions tab check the 'store' box.
Compile it, sign it and upload to Google play.
Lastly, the app has to be live on Google Play.
Now, it works to the point where you can purchase. A screen comes up and asks if you want to purchase. After purchase the screen goes away and that's about it.
The verification flags to pass onto C2 to see if an item is already purchased, needs refund, date of purchase etc. is not currently working.
Right now there seems to be a tug of war going on. Ashley mentioned he implemented the cocoonjs code for IAP and is waiting for Ludei to instruct how to use it.
Ludei on the other hand keeps pointing to their IAP wiki reference as instructions of how to use it in their forum. It's useless to us C2 folks since we can't access the info in C2 format.