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 it - even when I clicked "already have license (or something like that). I am NOT happy about this. If Poweramp has to check with Google Play to verify my license every time (or every 3rd or 5th or 10th time) then this is unacceptable and I would like my money back and I will remove it from my phone. Good thing I also installed free versions of JetStudio, Equalizer and Music Player which I wound up using the rest of the flight - they all worked fine.
I noticed two versions on my phone Poweramp (free) and Power amp (unlocker) which when I ran the unlocked version said I could combine the two.
I am returning to Boston in 3 days - so please send me a version that NEVER checks for my license (because you guys build that into the binary somehow) or fix the problem (assuming you know what this licensing problem is all about) or return my money.