Write to support@cypresstech.net. Please include the app name, the version from Settings → About, your phone model and what happened. The full rules are in the app at Settings → How to play.
By the solving techniques a puzzle needs. Easy and Medium need only single-candidate reasoning; Hard needs pairs and box-line reasoning; Expert needs more advanced patterns.
Expert is played without mistake checking by default. Turn on "Show mistakes on Expert" in Settings if you want it.
Press and hold the number until it stays lit, then tap the squares. Tap the number again to release it.
At midnight on your phone. It is generated on the phone from the date, so it works offline.
Settings → Remove ads. It is a one-time purchase, not a subscription, and it removes every ad. It does not unlock anything else, because nothing else is locked.
Open Settings → Restore purchase while signed in to the Google account you bought it with. If the price does not show, check that you are online and that Google Play is up to date.
No. The game screen never shows an ad. The free version shows a banner on menu screens and may show one full-screen ad after a game has finished.
Yes. Every part of the game works with no connection. Ads simply do not appear.
Only on your phone. There is no account and no cloud copy, so they do not move to a new phone and are erased if you uninstall.
No. The game is saved after every move. Open the app and tap Continue.
Starting a new game while one is in progress ends the old one and records it as a loss.
Where a consent choice applies to you, Settings → Privacy choices opens the form again.