- Depending on the smartphone app (which requires HFP (Hands-free Profile)/HSP (Headset Profile)), you may hear a voice from the left unit only, but not from the right unit.
- Check that the connected device and both the right and left units of the headset are turned on.
- Check that the headset and the transmitting Bluetooth device are connected via Bluetooth A2DP.
- Turn up the volume if it is too low.
- Check that the connected device is playing back.
- Pair the headset and the Bluetooth device again.