How to play
Every cell keeps its number, and there is no tool to pick. Tap a cell once for a green circle — kept — again for a red one — rejected, out of the answer — and once more to clear it back to undecided. No two rejected cells may touch, and the kept cells must stay connected.
Nothing here tells you you are wrong on its own, not even once the last cell is decided. Check names any rule your circles already break; solve it correctly and the board says so itself.