Both keys must be traded. Coral Crest Key first, Sealion Crest Key second. When you get the text " is holding the lock open...", that is when the Sealion Crest Key is traded. When the Coral Crest Key holder gets the message "'s hand has grown numb!" then it's too late to trade the Sealion Crest Key. make sure that whoever makes the first trade is ready to give a text signal i.e. "go" or "now" when you get the first text about the lock being opened.