Check the following:
Ensure that the app is has granted access to the audio devices.
Ensure that the app receives the onJoinChannelSuccess callback, which means users have joined the channel successfully.
Check if you muted yourself or others.
Check if you called the adjustRecordingSignalVolume or adjustPlaybackSignalVolume method to mute the audio.
Check if the recording device is working. You can call the startEchoTest method to test it.
Check if the headset is working.
Call the setEnableSpeakphone method and ensure that you cannot hear any voice from the headset when the speaker mode is on.
Check if the headset is working and if the audio output is set to the headset.
Test your device with the Agora Video Call demo (downloaded from Agora.io).
In Windows, if users cannot hear any voice from the speaker or headset: