You are out of moves. Instead of paying 900 coins, there could be an additional one-time option per level to give you another 5 moves (or maybe even only 3 moves) for a last effort by watching a 30-second ad.

Firstly, I believe that 900 coins is very excessive for a continue/life. 300 coins is reasonable without making it "free." You have to beat approximately 15 levels (18 max) for just one continue, and if you are stuck on a level for days with no coins because the level requires a great deal of luck, you have no way to proceed as a free player taking all of the fun out of the game.