I have connected a Sennheiser headset HD 4.40 Bluetooth to Ubuntu 20.04 but its microphone is not working. I can see it on the audio configuration window but the test bar does not move at all, it does not detect any audio. The headphones are working OK.
I am using a Plugable USB 2.0 Bluetooth adapter:
Bus 001 Device 002: ID 0a5c:21e8 Broadcom Corp. BCM20702A0 Bluetooth 4.0
Any ideas about how to fix this?