how to make grid location and sample texture kill particles in latest version of unreal

okay so i am using 2 grid nodes; spawn particle in grid and grid location (grid works as intended) and a sample texture node, in the sample texture node u can find “sample rejection” and i am stuck on as what to put in the “B value” i’ve tried multiple things (gridcellcoordinate, gridUVW, even more complicated structures using these) and even looked up a couple of tutorials and none of them seem to work

what do i put in B so that it goes over every particle looks at it’s location and checks with the texture for it"s black and white value there