Make sure that both Sound Input and Output is set to the VB-Cable in the sound settings on your operating system.
Set Operating Sound defaults to VB Cable
In your Browser Settings (the three dots at the top right of the Browser), double check that the Microphone is set to the VB-Cable as well. This is an example using Edge Browser.
Confirm that the browser is using the same VB Cable
Once done, your computer audio should feed into the Mona space directly (rather than use your microphone)