Carla is the security officer at the blimb boarding station.
She is using the metal detector to search those who try to go through the metal detector with metallic items.
Did you notice Manny will put all his items from the inventory on the table while Carla searches him. ?
You have to try to pass the bigger detector, so that Carla will do the search.
Well, Manny doesn't have any metal on him.
You would need to put some metal into Manny without it showing in the inventory.
Check out your Calavera Cafe. You will find something with metal, gold, in it from there.
Go downstairs at Calavera Cafe and into the bar. There is a bottle of Marillo de Oro. It has gold flakes in it.
Take it from the inventory and use it. Manny will take a sip from it. He now has metal in him.
Go back to Carla and let her search Manny. ?
Walk through the gate while you have sipped from the bottle.
Talk to her about the metal detector.
Go find the metal detector.