The connection procedure may be the cause.

You can't establish a Bluetooth connection with your mobile device from the settings screen of the mobile device when you have Bluetooth headphones, etc., connected already.

In this case, a message such as [Pairing Unsuccessful] or [Couldn't pair with DDJ-FLX2] is displayed.

Be sure to start the application before making a Bluetooth connection.

Note: You can't connect to a mobile device via Bluetooth automatically.