Bluetooth headphones can be used by changing the "Disable USB audio routing" setting in the developer options. 
Refer to the following guide Configure on-device developer options  |  Android Studio  |  Android Developers  to enable developer options on the Motorola Edge device.

  1. Open Settings > System > Developer options then scroll down far to Disable USB audio routing and enable it. (The setting can also be found via serarch)
  2. Restart your phone to make sure it takes effect.
  3. Connect the phone to your Bluetooth headphones. They can be used as usual now.