I just purchased Powersamp from Google Play yesterday for my Galaxy S6 and it ran fine. Today, I was on a plane from Boston to LA (6 1/2 hr flight) and was expecting to use it all the way. I started it before we took off and somewhere over Kansas - I exited the program and put my phone into airplane mode - NO internet connection.
When I restarted Poweramp - it gave me a message that it couldn't get to Google Play to verify my license - and locked me out. So this great program that I purchased was dead to me. I couldn't get past that message and, obviously, couldn't send an email from