Opened the editor, placed down a player. Added to init-line: this addAction ["Kill him!", "killhim.sqf"];
where "killhim.sqf":
dummy1 setDamage 1;
Then created a second unit in front of me named "dummy1". Created a trigger with activation: repeatedly,
condition:
!(alive dummy1)
onActivation:
hint "You killed dummy1!"
Exported the map, created a dedicated server, joined that server, used the action and everything works as it should.