Enabling killing of npc's for normal users?

Hello, I’ve had a recent problem with my server concerning npc’s over the past couple of hours. When I spawned an npc, only admins including myself were aloud to kill it. But when a normal user tried to kill it, it didn’t die. Is there a way I can enable this for users? I wanted to have a zombie apocolypse type of thing.

A command perhaps? Or server setting?

ULX is probably blocking it.

any commands…