We're aware of an issue with Facebook purchases for all King Games and our team is on it. 🛠️ Hang tight while we fix things! You can still enjoy the game, and we'll keep you posted once it's solved.
They are time-limited challenges. Which are given to the player at random. So you got it short and then it's gone. I have it very often. But it could come back and you'll have it longer. Just be patient.