No recording on instrument channel from ID4

I’m recording through an Audient ID4 audio interface, one instrument input and one vocal input. The ID4 is connected to the computer with a USB cable. The inputs are recorded individually into separate tracks in Audacity. Both inputs can be monitored on the ID4, but only the vocal input is captured by Audacity. The instrument input is not captured. I have reviewed all of the configuration options in Audacity, but can’t find a reason why one input can be recorded but not the other. I would appreciate any suggestions on what the problem might be and how to correct it. Thank you.