I've setup a systemd service file to perform some pactl operations at system startup for a test process. While the commands work fine when performed from a terminal I always get "pa_context_connect() failed connection refused" when running the same script from the systemd service by starting the service. I'm also using the 'User=' directive in the service file to ensure that the auto-login user matches the user used to run the service commands.
I've read that this is somehow related to the pulseaudio session not being valid in the environmentless context of the systemd service but I haven't been able to figure that out further.