How do I get more keys to go to chapter 5 in Trapmaker?

Are you asking about the keys you need from the main menu to unlock the next chapter, or a puzzle in the game?

If it's the ones to unlock chapters, aside from paying for them, you either have to wait the 3 hours for another key, or you can watch an ad, usually 30 seconds, to reduce your timer by 30 min (I think there might be a limit to haw many you can watch a say).

If it's a puzzle in the game, could you add more details?