I did the quest wonder manjin master got in exchange for a key and told me to go to the mountains manjin trapped in a cage that was key to the cage. Unfortunately, this key by accident I threw and I can not take the quest from manjin trapped in the mountains. and this quest with a key I can not repeat. Do you know where to get the key? or someone who has it?

Select the quest and click forfeit, then go to the wonder majin master and start the quest again.