Why isn't an Availability Status appearing on Performances even though I've created it?

Availability Statuses are set for the Venue Plan, not for the Event.

So if an Availability Status has been created through the Event page, it will need to be applied to performances for it to work.

You can do this in bulk via the Performances page for an Event.

If you'd just like to add an Availability Status to a single Performance, you can do this on the Box Office page.