I am implementing in-app purchase using https://github.com/anjlab/android-inapp-billing-v3 .
But while in app pop up open it shows "Error Authentication is required.You need to sign into your google account".
I tested using different devices as same result.
Improtant ! I've spent a lot of time trying to find out why I'm getting error "Error Authentication is required.You need to sign into your google account". And after a lot of hours I found out - I was trying to access wrong item id from the console. In the developer console subscription item had id "premium" and I've tried to access "premium_version" item. Stupid mistake but error from google is absolutely not informative. Hope this helps