If you're not getting audio from a connected Bluetooth device:
Disconnect anything connected to the speaker's aux jack. When the aux jack is connected, Bluetooth is disabled.
Go to the device's Bluetooth settings and make sure that it is connected to the speaker
Make sure that the speaker volume is turned up. Set the Bluetooth device's volume to 90% and then use the Bose speaker volume controls to adjust the level
Try playing a different source on the Bluetooth device. For example, try a different app to determine whether the issue is with a particular app
Your Bluetooth device may be out of range. Try moving it closer to the speaker
In the device's Bluetooth settings, choose to "FORGET" or "REMOVE" the Bose speaker. Then, pair the device to the speaker again and retest
On the speaker, press and hold the Bluetooth button for 10 seconds to clear the Bluetooth device list. Then, pair the device to the speaker again and retest
Reboot the Bluetooth device. This is typically done by shutting it down completely and then restarting it
Reboot the speaker by disconnecting its power cable for 30 seconds.
Try a different Bluetooth device to determine whether there is an issue with the device