WiiM Amp: Optical In not working

[playtheorchestra]

I have the WiiM Amp running firmware 5.0.739659.

In the app, after switching to Optical In, it briefly says "Detecting Audio" and then says "No Audio".

• I've tried different CD players, and different optical cables, and cannot get the Optical In to work.
• I also have 2 WiiM Amps, in different rooms, and am unable to play from Optical In other either one.
• I've made sure the cables are seated on both the player and Amp, and that music is playing.
• I have Auto-sending of Optical In on.

I have confirmed Line In from the same source(s) is working.
But I would prefer Optical In if possible.

Is there another step I am missing? Thank you.

 

[goodmore]

Not sure , but does the music source have to be set to PCM output.