Rhino 6: Snapping solid objects not working

Hey all! I’m new to learning Rhino, spending quarantine learning it, and trying to figure out how to snap.

I want to snap an extruded wall to be on the same “floor” plane as the staircase I already built, and I also want to butt the wall up to the back of the staircase… No snapping is working! Everything is turned on, I’ve looked on all the existing forum questions and messed with all the settings… nothing. File is attached.

Thank you!

snap test_hcook.3dm (12.0 MB)

have you tried using the Tab key to lock the direction?