Some of the passengers encroach any of the parts of neighboring seats on the aircraft due to their size. Southwest Airlines understands this thing and that's why it offers a passenger a comfortable journey by allowing an extra seat purchase on their flight. The passenger may proactively purchase a seat prior to the travel so that the airline can make the needful and plan a Southwest Airlines booking adequately.
As soon as you complete the payment for Southwest Airlines flight reservations, you would get a confirmation on your email account. You also will get the booking reference number in that email, which will let you access your flight bookings later.
This is how you will be able to book an extra seat for a passenger under the customer of size policy of Southwest Airlines. Moreover, if you see any kind of problem while doing the reservations on Southwest Airlines, you have to contact the reservation support team. The team is one call away from you to make Southwest Airlines booking. So, at any time call the customer service and book the extra flight tickets