Apps Debugging Google Play Purchases


I have a task to upgrade an app to use the Google Billing API for allowing the user to purchase a one time premium item for a small amount. The documentation on the code was pretty clear and I implemented it, but I was told that it doesn't work for new users to buy the product (and somehow existing users lost their premium status, but that's something else).
I have to look further into that, but I still dont get how to test the purchase flow while debugging the app from Android Studio. When I try to purchase, Google tells me that the app version is not configured for Google Play payments.
I think that I've already configured myself as license tester in the Google Play Console.
Can anyone help?