Why isnt the Subtraction not working?

I am trying to make a doorway, and am using the Box set as a subtract. But the section I want removed is not being subtracted.

I’m having the same issue. If I find anything I will get back to you.
(UPDATE)
Try deleting the wall you are trying to subtract from and use the box brush geometry. The issue I had was that I was using the original box that you get when you open and start a new level. It will not let you subtract from it maybe because it has other surface materials built into it already, but don’t quote me on that. I used that original box to build my walls by duplicating (alt+drag). Once I deleted the wall I was trying to subtract from and added in the new box geometry in its place, it would then let me subtract from this surface. This worked for me. Hope this helped.

I think you can only use brushes on other brushes, not on static meshes

Issue still not solved. Using 4.25 substractio not working at all after multiple try.