To fill out Advance Passenger Information (API or APIS), you typically log in to your airline's website or mobile app and navigate to the "Manage My Booking" section. You will need your passport or travel document ready, as the system requires your full legal name, date of birth, gender, nationality, and passport number/expiry date. Many airlines in 2026 use automated passport scanning via their apps to ensure data accuracy and speed up the process. It is a legal requirement for international travel to countries like the U.S., UK, and EU, and must generally be completed at least 72 hours before departure or during online check-in. This data is transmitted through a secure network to government border authorities to facilitate security screenings and identity verification before you even arrive at the airport, helping to maintain a high level of global travel security.