So im trying to make a hallway with a light that's a little lower than the ceiling so fluid can flow through the crack but the fluid goes right through it. I have it set to effector. I used the knife project tool to cut the hole on top.
The problem is that the collider's normals are inverted.
In solid view with the domain hidden, you can turn on the face orientation overlay to display the front of faces as blue and the back of faces as red.
As you can see, the collider's faces are facing inward:
To fix this problem, select the object enter edit mode, select everything, then press ShftN to recalculate the normals.
After doing this, the collider will work.
To get the simulation fine enough to flow through the cracks, I set the domain resolution to 256.