You can save the time and hassle of paying for baggage fees at the airport by pre-paying online. You can do this on the American Airlines app or using their website when you check in, which can be done up to four hours in advance of your flight. Be aware that if you're checking more than three bags for your flight, you'll need to pay at the airport. You can pre-pay for your luggage using a credit card or wait and pay cash/credit card at the airport.