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.
• Depending on the smartphone app (which requires HFP (Hands-free Profile)/HSP (Headset Profile)), you may only hear the voice from either the (L) left unit or 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.
• Turn the headset off, and then on again.
  Put the headset in the charging case and close the cover. Then remove the headset from the charging case and confirm that the indicators (blue) on the (L) left unit and (R) right unit are flashing.
• Reset the headset.If resetting does not work, initialize the headset.For details about resetting and initializing your headset, refer to the Help Guide supplied with the headset.