Mindfret is made by one person. Write to support@mindfret.com and you will get a reply, usually within a few days.
Tap Get Pro at the top of the home screen, or any tab marked PRO, and choose Restore purchase. Mindfret Pro is a single payment tied to your Apple ID, so it comes back on any phone signed in to the same account, at no further cost.
If it still does not unlock, check that the phone is signed in to the Apple ID you bought with, then write in.
No. Mindfret Pro is a single payment ($8.99 in the US) and there is nothing to cancel. Nothing you have unlocked is ever taken away, and there is no second payment later.
Refunds are handled by Apple, not by us: we never take the payment and cannot reverse it. Go to reportaproblem.apple.com, sign in and find the purchase there.
Settings, behind the gear at the top of the home screen, has Reset a tab. Each of the four resets clears only its own tab, so redoing the neck does not cost you your chord grips. Each one takes a second tap to confirm and cannot be undone. Your day streak survives all four.
Untick Anonymous usage data in Settings and the app stops sending; nothing else changes. What that data is, and is not, is set out in full on the privacy page.
Only to buy Mindfret Pro. Every drill, map and progress screen works with the phone in aeroplane mode, because your whole record is on the device.
There is none to make. Open the app and start. The consequence worth knowing: because there is no account, there is nothing holding your progress but the phone itself. Delete the app and it is gone.
Please write in, with the tab and a screenshot if you can. A wrong note or a wrong shape is the most serious kind of bug this app can have, and it gets fixed first.