Wire cut a closed poly surface

i am trying to wire cut the part in green but I can’t get it to work.
I drew a line in the shape of an “L” to where i want to take a section out of the green part. I think I am taking the correct steps but nothing happens
test-3.3dm (329.5 KB)

i thought the line would work, after watching the help file animation i made my lines in to a square shape and then it works.

A line does work, you just need to do it from an ortho view and set the direction to be normal to the cplane.

thanks!, that works.