Listeners pick a language and turn on audio, but hear nothing.
Most likely: the language has captions but no voice
Check: in the Console, the language's row shows CC ONLY. Captions reach every language, but only a channel with a voice can be heard.
Fix: open the channel's ⋯ menu and select Turn on the AI voice for the language, or Assign a human interpreter to it. See Voices in the Console.
Next: the voice is starting, paused or down
Check: the row's tag. starting means people just turned on the audio and the voice takes a few seconds to start. Paused, voice paused or voice down mean the voice is not speaking.
Fix: wait a few seconds for a starting voice. For the others, see A voice went silent.
Next: the session is not live
Check: the Console shows Off air.
Fix: listeners hear nothing until the session goes live. Select Go live, or wait for auto-start.
Next: the listener's phone
Check: the phone's volume, its silent switch, and whether its audio goes to headphones or a speaker that is off.
Fix: turn the volume up and the silent mode off, and check where the phone sends its sound. If it works on mobile data but not on the venue Wi-Fi, the venue network is the cause.
Still not working
In the Console, select Listen to it in the channel's menu to hear the channel yourself. Contact support with the time, the session and the language.