The most common cause of this issue is the wrong selection of audio output. 

The WiiM Mini only outputs the audio in one of its analog audio (Aux-out) or digital audio interface (SPDIF). When the Aux-out interface is plugged into audio cable, it'll be automatically switched to Aux-out. 

The WiiM pro can output the audio in one of its three output interfaces: Line out, SPDIF out and Coax. Please check which audio output is active first.,

Check the active audio output

You can check the active audio output by selecting the Device tab > Device setting gear icon > Audio Output.  make sure you're using the right audio output and connect the audio cable tightly? 

Check the optical signal and output resolution if using optical SPDIF output.

If you choose the SPDIF optical output, please check if you can see the 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 get in touch 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 the device tab > tap device setting gear icon > Audio Settings > SPDIF Output resolution

If you can't hear 192kHz and 24-bit audio, please choose 96 kHz to see if you can hear the test audio. 

You can select the sample rate and bit depth pair and see what the maximal audio resolution your system can support.