It should come automatically, though it does seem odd that it’s out of phase with your others. Personally I’d give it a couple of days, and then raise a support ticket.
I’m having the same issue as the others. I have two XTs and one indoor connected right now to the same sync module. I only have one XT that has the activity zone option. Still waiting for the other XT to get the setting.
Love this feature. Stops alot of false motion detection (moving bushes… dog path). Would be nice if the boxes were even smaller for better fine-tuning grayed out zones.