Is this a game mechanic or a bug?

[小小界]

My friends and I play online together, and finally the two goals of customs clearance have been achieved, but to clear the customs he said to find the key to clear the customs, we looked for a long time is not find,is the bug or we really did not see it? Finally, I searched the walkthrough video and found that everybody else had ended the game after finding the crown,so i wanted to ask if this was a bug or if we really, really didn't find the key.

[Bill Simmons]

There is in fact a key that will open the exit. Finding it may be tricky, but its location is in a room of great importance. Look upon the furniture in the room, for laying atop one piece is the key to escaping with your goods.

The walkthroughs you viewed were likely from the demo, which ended as soon as the vault was opened. The prologue (this version) requires a couple more steps to reach the end, but not many.

Good luck in your future endeavors

[Raven]

Thanks Bill for this perfect answer!
I wouldn't have said better!

[小小界]

Ok, thank you very much for your answers.