Your first flight is not operated by American Airlines. You're traveling with a pet, weapon or firearm. You're an unaccompanied minor. It is not 1–24 hours before your flight within the U.S., Puerto Rico or the U.S. Virgin Islands or 2– 24 hours before your international flight.

There are several common reasons why American Airlines (AA) might block online check-in in 2026, with the most frequent being a mandatory document verification. For international flights, the airline must often visually verify your physical passport or visa at the airport counter to ensure you meet the entry requirements of your destination. Another common reason is that you have been selected for Secondary Security Screening Selection (SSSS), which requires a manual boarding pass printout after an enhanced security check. Technical issues can also occur if your "Secure Flight" data (name, date of birth, gender) does not perfectly match your ID, or if you are traveling on a codeshare flight operated by a partner like British Airways or Iberia. If you are traveling with an infant-on-lap or require special assistance, AA often requires an in-person check-in to ensure all safety protocols are met. Finally, if the flight is overbooked, the system may prevent online check-in to manage "standby" lists more effectively. If you see this error, it's best to arrive at the airport 3 hours early for international or 2 hours for domestic travel.