I had a similar experience: I was trying to play sound over bluetooth with a raspberry pi zero w, on rasbian lite (headless) stretch.
Having read that you should use
pulseaudio, since "the bluetooth stack" aka
bluez doesn't support
ALSA anymore, I saw that the above error message (protocol not available) disappeared whenever I had pulseaudio running, with certain bluetooth modules loaded (
module-bluetooth-discover), and I was able to connect and maintain the connection as well as use the bluetooth device as an audio sink.
But I couldn't get pulseaudio to run properly when deploying it as a service, neither in system-mode nor in user-mode... finally I gave up, especially since I discovered a project that brings back integration of bluetooth with alsa directly, and which is available in the standard repositories as
So since I unfortunately can't comment, this half answer is saying: If you're using pulseaudio, make sure to start it manually with modules loaded. Otherwise I suggest using
bluealsa. And as far as I understand, the error message is telling you that it doesn't know how to handle this
A2DP thing, which should give you a clue - have something running that knows how to communicate with devices through the