I could not get it to work; I'm not even sure if I did it right.
I assume what you need to do is:
1. take your product id, which you can do it in google play console, and put it in the plugin.
2. put your Google Play's Public Signature in Cocoonjs Cloud Compiler.
and cocoonjs should do the magic when you use Cocoonjs IAP plugin, like purchase with preview(id). But so far, nothing works for me :(