From Southwest.com: https://www.southwest.com/airfare-ty...tandby-change/


Why am I being directed to speak with a Southwest Customer Service Agent at the airport?

You may need to speak with a Customer Service Agent to be added to the same-day standby list for a variety of reasons, including, but not limited to:

You are attempting to add yourself to the same-day standby list less than 30 minutes prior to your desired flight's scheduled departure.
Your desired itinerary change may result in a collection or refund of taxes and fees.
You are traveling on an international itinerary.
Your desired itinerary change will result in a different connection city than your confirmed itinerary.
You are attempting to add yourself to the same-day standby list in your connection city.
You are trying to list for a flight later than your original flight.
Keep in mind that group bookings and Unaccompanied Minors are not eligible for same-day standby.