TLDR: please use Settings / Restore Purchase.
You can restore Premium purchase any time for free as long as you use the Google account you bought it with. Note that for Google Play Store purchases, if you have multiple google accounts on the phone, your "original" Google account should be selected in Play Store (top-right icon / Manage Accounts).
You can check if purchase is valid for your account here: https://play.google.com/store/account/orderhistory?purchaseFilter=apps
To restore purchase, please:
- ensure you have Internet connection on the device (you can open https://powerampapp.com)
- ensure you have Poweramp Equalizer uni build from Poweramp website (e.g. build-900-arm64-uni). Play builds don't have non-Play purchase support, but Play builds can be installed over website version and license will retain.
- in Settings use Restore Purchase / Website and type in that Google or Email account and Order ID (as specified in purchase confirmation email from PayPro Global).