Let me be more specific. After you buy your ticket online and put in on hold, call aa.com tech support at 800 222-2377. (This is a published number.) They will give you an address in Florida to mail the voucher to and tell you exactly what to write on the outside of the envelope to have it credited to the right ticket. Total cost is 37¢ in the U.S. unless you also have to buy an envelope, in which case it's about 40¢ depending on your taste in envelopes and how many you buy at a time. (Both of those go up by 2¢ early next year.) There is no need to pay any fee, let alone get to an airport, unless you're flying within the next few days.