Multi mic Zooming with a Tascam DX40 and other USB interfaces

Hi everyone, first time poster to the forum here.

I was wondering if anyone uses a USB audio interface whilst on Zoom. I was testing out a Tascam 4 channel audio recorder today and tried to run two radio microphones through it. Both were picking up on the Tascam however only one was being streamed through Zoom. Is this an issue with Zoom needing to be in stereo? if so how do I change it and does anyone else Zoom this type of set up is so what equipment do you use?

Thanks in advance!