There are no free pairs left. It happens, and that is perfectly fine. You can shuffle the remaining tiles so the game can be solved again, or undo a few moves.
Rules
The goal is to clear every tile from the board, two matching tiles at a time.
Free tiles
You can only take a tile when it is free. No tile may lie on top of it, not even partly, and it must have an open side to the left or to the right.
What matches
Identical tiles match: the same suit and the same number or symbol. All flowers match each other, and all seasons match each other.
Good tips
Take tiles from the high layers and the long rows first.
Hint shows a possible pair. Undo works as many times as you like.
If you get stuck, you can shuffle the remaining tiles.