This error means license can't be verified due to:
internet connection abruptly stopped during activation or it's not possible to establish secure https session.
Please try to activate again
you're behind some router which requires authorization and redirects to some login web page.
Please try to open any site in a mobile browser first
Poweramp APK is not genuine (hacked, moded).
Please download and install Poweramp APK from https://powerampapp.com