There is no sound.

Try the following:

• The smartphone and the headset (both the (L) left unit and (R) right unit) are turned on.
  When the battery of the headset is completely discharged, the headset turns off automatically. Place the headset in the charging case and allow it to charge.
• When the sound of the headset is too low, turn up the volume on the smartphone.
• Voice guidance, ringtone, and voice call can only be heard from the (L) left unit.
• Depending on the smartphone app (which requires HFP (Hands-free Profile)/HSP (Headset Profile)), you will only hear a voice from the (L) left unit, and not from the (R) right unit.
• The headset and the smartphone are connected using a BLUETOOTH A2DP connection.
• The smartphone is playing back correctly.
• Delete the headset information from the smartphone, then pair the headset with the smartphone again.
• In the configuration of the headset, transmission between the smartphone and the (L) left unit of the headset is prioritized. In areas with poor signals, such as locations with many Wi-Fi connections, the sound may be temporarily interrupted in the (R) right unit of the headset only.