Sorry it’s not working for you, it all hangs on having a decent room scan for mixed reality (I assume you’re on a Quest 3).
Here’s another way you can set it up - set up a room scan using the meta menus, here’s a video on how to do that:
https://youtube.com/shorts/O9gGMHCEpWo?feature=share
Once you have a room scan, select the ‘use current scan’ option when it appears in the game.
Let me know how it goes 👍