Background
 
The most common cause of this issue is due to the wrong selection of audio output. The WiiM Mini only outputs the audio in one of its analog audio (Aux-out) or optical digital interface. When the Aux-out interface is plugged with audio cable, it'll be automatically switched to the analog audio output.

How to know which audio output is active

You can check the active output port by selecting the Device tab > Device setting gear icon > Audio settingsAudio output and make sure you're using the correct audio output and the connect cable is tight. 

No audio from the optical output

If you ensure the active audio output is SPDIF optical output, please check if can see red laser light from the optical port (please don't watch it directly) if you're playing music. If there's no red laser light, the port may be broken and please contact with us or your seller. 

If there's red laser light but you still can't hear sound, please try to play the test sound on the WiiM Home app. Please select device tab > tap device setting gear icon > Audio Settings > SPDIF Output resolution Then select the sample rate and bit depth pair and see what's the maximal audio resolution your system can support.