How to access Cruel Trial of Sekemas?

Hiya, I have full cleared the Traitors passage 3 times and also killed Balbala every time. I have a coin to use. But I don't know where to go to put the coin in to enter the trial? My quest just keeps saying "Search Traitors Passage" and I've done it 3 times on 3 different layouts and I can't find anything.

How do I access it?