I went back and checked and that was one of the earlier doors. The beginning of chapter 40.1 shows them passing through the door to the trial room normally. That would have been a good way to get them out of the contract, though.Wait, is the contract they "signed" the last door that was cut apart?
Because if so Merchant-san and Lavi didn't sign it. Lol
Or was it one of the earlier riddle things they based by?