What does it mean that the Defend Carrot level has not been unlocked yet?

Failed to pass the previous level. In the Defend the Carrot game, you have to pass one level before proceeding to the next level. When the previous level is not passed, the next level will be displayed as not yet unlocked and cannot be played. "Defend Carrot" is a cute-style tower defense game developed by Feiyu Technology (Kairo World). It is easy to play, suitable for all ages, and has built-in novice guidance.