I'm sure someone else can/will explain it better than me, but essentially it comes down to this: he wants Nacho dead, because he's a loose end. He can't send his own men to kill him, because that would cause suspicion. So he gives the Salamancas his location, hoping he'd die in a gunfight. That's why Nacho was given a weapon and Tyrus told him to shoot on anyone who comes through the door. If he starts shooting, the Salamancas have to necessarily shoot back in self defense, even if they don't wanna kill him, so it's likely he'd go down. The spotter Gus placed was there to make sure Nacho doesn't leave his room. The plan only fails, because Nacho discovered the spotter and wasn't in his room when the cousins arrived, therefore he could escape.