Hi, This is usually caused by not having exported the DISPLAY variable into the systemd environment, there has been extensive discussion about this in #347[1] upstream. How are you starting X11, are you using a custom xinitrc?
However it is weird that systemd reports that dunst is running even though it obviously fails to start. I'm not sure what is going on there. [1] https://github.com/dunst-project/dunst/issues/347
