ERROR_NOT_MARKET_MANAGED in com.google.android.vending.licensing

So, after spending more than a day scratching my head over the fact that I constantly got the error code: ERROR_NOT_MARKET_MANAGED returned via my callback in the Google licensing API, the solution, as it usually does, turned out to be a simple answer.

Regardless of the fact that all Googles developer documentation tells you it's good enough to upload your APK to the product page for license testing to work, this is not true.

To get it to work, you need to publish you app. At first thought, I was afraid this would make it "live", but as long as your APK is in the Alpha or Beta Testing section, you'll be ok.