Only headphone sound

I have just received my QC. Connected by USB to my macbook pro m1 and to my powered monitors through output 3&4. I want to play together with backtrack files from my mac, Chordify etc. I only hear sound through my headphones connected to my QC.
Yet when I play my guitar I can it through the monitors. What am I missing?
Thank you

Problem solved by using usb and main out 1&2 (xlr).