Set Plane or Quad to black for transparent background

I’m developing an AR app for the Meta2 AR headset where black is supposed to be transparent and not rendered. I want to display my augmentations on the black plane so only the augmentations are visible, but the black plane is being rendered as a black plane, not transparent?? What do I need to do to make the plane black for transparency in Unity.

Change material-shader = transparent. or adjust material.color.a =0 where a is Alpha value