PrimozRome

Maybe it's just me but I don't know how to paste B&W image into layer mask? I use KeyShot to render our models, and keyshot can render image and it's mask image separately into two different image files. I need to create mask image file and paste it into mask in the Affinity Photo. This is an easy task as copy paste in photoshop, but can't get it working in Affinity Photo. Any suggestions?