No audio signal passing? Our advice is to check the most obvious, “it can never be that” thing first…which usually means a cable.
Real-world example: we were setting up a rig consisting of a guitar, pedalboard, and amp. No sound was passing. After several minutes of pulling our hair out, checking every power connection, every pedal, every volume knob, we realized that the cable wasn’t plugged into the guitar’s output jack. Doh!