Email support@tapertrophy.com. A person reads it. Expect a reply within a couple of days.
If you've reinstalled the app or moved to a new phone, open the app and use Restore Purchases. It appears anywhere the unlock is offered. Your purchase is tied to your App Store or Google Play account, so it comes back as long as you're signed in with the same one you bought it with.
Everything you log is stored on your phone and nowhere else. That means it doesn't sync between devices, and if you delete the app the log goes with it. Export from the app before you uninstall if you want to keep it — export is free whether or not you've purchased.
The app compares recent training against your longer-term baseline, and that baseline takes about four weeks of logging to fill. Before then it says so on screen rather than pretending to know more than it does.
Tapertrophy estimates readiness from what you log. It cannot measure anything about your body, and nothing in it is medical advice. If something feels wrong — pain that isn't normal soreness, fatigue that won't lift — talk to a doctor or a qualified professional.