Sunny Sort has no account and no server, which rules out a whole category of problems. Here is the short list of everything else.
Check the ring/silent switch on the side of your iPhone. Sunny Sort respects it like most games do, so a silenced phone plays nothing even with the in-app sound turned on.
If the switch is already off, open Settings from the title screen or the pause menu and confirm Sound is on.
Progress is stored on the device, not in an account. Deleting the app deletes it, and it does not transfer to a new phone.
It is never uploaded anywhere, so there is nothing for us to restore. If progress vanished without the app being deleted, tell us which level you were on.
No shipped level is unwinnable — each one is solved by a search before release, with at least two moves of slack beyond the shortest solution.
If a level genuinely will not go, send the level number. That is a bug worth a fix, and the number is all we need to reproduce it.
Running out of free cells is the losing condition, not a bug. A pile parked in a corner is a cell you do not get back.
Restart from the pause menu; the level is identical every time, so a plan you work out will hold.
iPhone on iOS 15 or newer, portrait only. iPad is not supported yet.
The app is offline, so no connection is needed at any point.
Send what you saw, the level number, and your iOS version. A screenshot helps more than a description.
Every rule bug becomes a test before it is fixed, so the report goes straight into the suite.
There is no ticket system and no bot — mail reaches the developer directly. Include your level number and iOS version and you will usually hear back within a couple of days.