a2dp-sink profile connect failed

I was able to solve the same problem on Ubuntu 21.04 based on this solution:

Adding the module-bluez5-discover at the end of the pulseaudio /etc/pulse/default.pa config:

load-module module-bluez5-discover

Restart PulseAudio:

killall pulseaudio

I have the exact same problem a2dp-sink profile connect failed + blueman.bluez.errors.DBusFailedError: Protocol not available.

I think the problem might be in our ~/.config/pulse/default.pa

#!/usr/bin/pulseaudio -nF
#
# Work around for PA not allowing access to A2DP profiles in the user session
# because GDM already has it open.
# LP: #1703415

# load system wide configuration
.include /etc/pulse/default.pa

### unload driver modules for Bluetooth hardware
.ifexists module-bluetooth-policy.so
  unload-module module-bluetooth-policy
.endif

.ifexists module-bluetooth-discover.so
  unload-module module-bluetooth-discover
.endif

As I do not reproduce the original bug listed in this workaround ( https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1703415 ) I think it can be safely commented :

#!/usr/bin/pulseaudio -nF
#
# Work around for PA not allowing access to A2DP profiles in the user session
# because GDM already has it open.
# LP: #1703415

# load system wide configuration
.include /etc/pulse/default.pa

### unload driver modules for Bluetooth hardware
#.ifexists module-bluetooth-policy.so
#  unload-module module-bluetooth-policy
#.endif
#
#.ifexists module-bluetooth-discover.so
#  unload-module module-bluetooth-discover
#.endif

then restart pulseaudio with

$ pulseaudio -k

It's also possible that this problematic workaround is not present in a fresh install of the latest Ubuntu release, I did not check. (I'm currently in 20.10, coming from an install in 18.10)

In my case(Ubuntu 18.04/Awesome wm), pulseaudio-module-bluetooth is already installed too.

Run the following commands to fix permissions:

sudo chown -R $USER:$USER $HOME/
sudo apt-get --purge --reinstall install pulseaudio-module-bluetooth alsa-base pulseaudio
mv ~/.config/pulse ~/.config/pulse.old

Then reboot your system.

Run the following commands:

sudo apt-get install pulseaudio-module-bluetooth
sudo killall pulseaudio
pulseaudio --start    
sudo systemctl restart bluetooth

Looks like something wrong was with module loading. I didn't really figure the reason, but I made i3 to load them manually on startup.

Add these lines to ~/.config/i3/config

exec --no-startup-id pactl load-module module-bluetooth-policy
exec --no-startup-id pactl load-module module-bluetooth-discover