Why I Can Only Get Mono Audio From The Switcher

You need to input stereo audio, The switcher can’t split mono audio to stereo audio. Please also be noted to select R/L for your audio option so that you can hear stereo audio

R/L : left and right channel audio are separated
L+R: left and right channel audio are combined
L=R: you will hear right channel audio for both left and right channel
R=L: you will hear left channel audio for both left and right channel