[Cinemachine] Rendering 2 cameras at the same time (1 for background depth of field)

I can't seem to get 2 cameras to render at the same time.

I have the main camera with a cinemachine brain. Culling mask is set Default layer ( to render everything but the background).
I then have a second camera (or blur cam) with a cinemachine brain. Culling mask is set to Background layer. ( I want to blur this layer with post processing.

However, the 2 cameras with brains don't render together ( like they do with default cameras).

Is this even possible with cinemachine?

Do I need 2 brains?

Do I have to clear some sort of flag?

Send help!

Youtube video link of issue

 

Okay, so I had a background image obscuring the other layer. I can now see the cameras rendering together!