I have an issue with the saber plugin

[Zac25383936x9dz]

When I added saber to my clip (that I used rotobrush on) I went to enable 'layer mask' but it didnt mask my layer it just stayed the same, as seen in the provided images. I was wondering if im doing something wrong or if it was a bug.

[Mylenium]

Pre-compose the RB layer, apply Saber and set its mode to contours in the parent comp. You may want to study a few tutorials.

Mylenium

[Zac25383936x9dz]

Whats an rb layer