Cracked Play always returns wrong signature for any Play response (even if app legally purchased). LuckyPatcher changes core Android files, so any signature checks via Android core are OK (this is a huge hole in your system as any app can replace e.g. system apps and do anything with the phone).
As Poweramp doesn't check signature using Android core and is not affected by LuckyPatcher "fix", this disables Poweramp ability to check valid purchase license.
Please disable LVL emulation, Google Billing Emulation (or other similar switches) in LuckyPatcher (or un-patch Play / core.jar - if modified Play is used and depending on LuckyPatcher version) in LuckyPatcher options for at least a day (24 hours) - so Poweramp is able to check itself (License Verified appears in settings).