Try these troubleshooting steps if your Echo device doesn't connect to an external sound system or Bluetooth speaker.
Echo Devices connect to many speakers over Bluetooth.
Keep in mind that Echo Dot only provides audio output to other speakers. Echo devices don't support Bluetooth speakers that require a PIN to pair.
To connect to a Bluetooth speaker proceed in this way:
Try to connect another device (like a smartphone) to the speaker.
Make sure to unpair other devices from the speaker.
For portable speakers, check the batteries for the speaker.
Check for interference. Move your Bluetooth speaker and Echo device away from sources of interference, such as microwave ovens, baby monitors, and other wireless devices.
In the Alexa app, forget the Bluetooth speaker. Go to Settings > (Echo Device Name) > Bluetooth in the app, and then select your Bluetooth speaker. Select Forget Device to unpair the speaker from your Echo device.
Try to reconnect to the Bluetooth speaker to your Echo device. Set the speaker to pairing mode, and then say, "Pair."