Apple (upper left) > System Preferences > Hardware > Sound > Input.
Is your device listed there? Does the blue dot sound meter jump when you play music? If not, then you are not presenting music to the Mac. Actually, better, if you can see your USB device in the list, you are not presenting sound to the USB device.
Do you get the green signal lights flashing on your US200? I’m guessing no.
Yes under Hardware > Sound > Input my US 200 is selected.
No dots jump about tho when I play music. I am running monitor speakers RKR Rokit 5. These play music from my mac or turntable via the DJM 400 mixer and US 200 which is USB to the mac, but on the Tascam US 200 the controls on the front Level > Mon Mix > ETC don’t seem to be working.
Also in the sound settings on the mac I cannot control the volume or mute etc the only way to control the volume from the monitor speakers is turning them from the rear of the speaker itself.
The only light on the US200 is a green USB light and that is it.