With a PC or Mac, this usually results from the input audio pointing at the wrong device in the device OS settings. It is advisable to check that also the Glue audio settings are set to the correct audio device. Note that if you use a PCVR device as a headphone while in desktop mode, you must have SteamVR running for the audio to work.
With standalone devices, the usual case is that during the initial Glue setup, the user did not permit Glue to use the device microphone. That can be reversed in the device settings.
A known issue is that sometimes a standalone device gets muted even though the audio settings are all correct. The workaround is to go to Glue audio settings, set it temporarily pointing to any other device in the listing, and then set it back to the Android audio device.