Years later I wanted to update my little game. I migrated my IAP codes to the new Google IAP plug in. But now, while testing on device, I got this error:
“Error 3, Google Play in-app Billing API version is less than 3”
Take a look at this and see if it addresses your issue.
Thank you very much Colin. I got the same warning in my inbox tbh. So I need to upload a new alpha or beta version to Google Play then? Do I understand correctly?
Probably. 
OK. I solved the problem. I wasn’t logged in to Google Play. Once logged in the error went away. what a strange error…