itch.io

there's requirements you must do before enslaving them. it says it when you do want to. and for the non-inmates, a collar must be bound on them

The game generates you a special tascks. You need to fulfill them before kidnaping NPC. You can see what you need to do in "Encounters" list, where your NPC is. Guards, engineers and nurses, must have specil collar on them as another user mentioned before me. You can obtain it at the arena, just talk to a anouncer and he will explain everything.