The Bluetooth connection attempt fails.

Try the following:

• The Headset may already be connected to another device (such as a smartphone). Disconnect the Bluetooth settings for devices other than the device to which you want to connect.
• Turn on the headset to which you want to connect and bring the headset and the smartphone within 1 meter (3.3 feet) from each other.
• Turn off the headset, and then turn it back on.
• Turn off Bluetooth connection on the smartphone, and then turn it back on.
• From the smartphone's Bluetooth setting menu, re-select the device information for the device to which you want to connect.
• Turn off the smartphone, and then turn it back on.
• Reset the headset.For how to reset the audio device, refer to the Instruction Manual.
• Uninstall Music Center / Headphones Connect, and then re-install it.
• Dear iOS 13.0 or later User,
  Permit access to [Bluetooth] from [Settings] - [Music Center / Headphones] on the iPhone.
  
• For iOS 11 user,
  When the app asks "Turn Bluetooth on?" frequently, try followings from "Control Center".
  1. Turn Airplane mode OFF.
  2. Turn the Bluetooth settings OFF, then ON.

If you cannot connect to the audio device using the methods above, try the following operations.

1. From the smartphone's Bluetooth setting menu, delete the device information for the device to which you want to connect.
2. Initialize the headset. After initialization, it will enter pairing mode. For how to initialize the audio device, refer to the Instruction Manual.
3. Use Music Center / Headphones Connect to make a Bluetooth connection.