Yamaha MG20XU No Playback

Hi all,

Trying to do some cross country collaboration here with a track some friends sent me. My interface is a Yamaha MG20XU USB mixer. When I’m plugged in/recording I can hear the mics in my headphones which are plugged in to the “Phones” jack on the mixer… However I need to dub on top of the track my friends sent and I can’t get it (the track sent to me) to produce sound in the headphones. The monitor is lighting up but it’s not coming through to the cans. Overdub is checked off on the menu. Line in and line out are both to the mixer, although when I turn off the mixer and disconnect the USB the computer speakers immediately start to work for playback.

Am I allowed to bump this?