During a recent trip with Aer Lingus, I ran into an issue that many other travelers seem to experience—I couldn’t check in online. If you’ve ever asked yourself, “Why will Aer Lingus not let me check in online?”, you’re not alone. When I tried to check in through the Aer Lingus website and app, I kept receiving an error message that said check-in was not available for my booking. At first, I thought it was a technical glitch, but after contacting customer support and doing some research, I discovered that there are several reasons why online check-in may not be available for certain Aer Lingus flights. One of the most common reasons is if your booking includes a flight that is operated by a partner airline or is part of a codeshare agreement. In this case, the check-in process might need to be done through the operating airline, not directly with Aer Lingus. Another reason I learned is if your itinerary involves traveling to or from the United States, because Aer Lingus sometimes requires manual passport verification at the airport. Also, passengers with special requirements—like those needing wheelchair assistance, traveling with pets, or flying with infants—are often required to check in at the counter to ensure all details are handled correctly. In my situation, I had a connecting flight through another airline, and that was likely the reason I couldn’t check in online. Additionally, some group bookings or reservations made through third-party travel sites may not qualify for online check-in due to booking system limitations. I also found out that passport or visa issues can trigger blocks in the online check-in system. If your travel documents are incomplete or haven’t been verified previously by Aer Lingus, you may be asked to check in at the airport. Another possible reason is if the airline system randomly selects you for additional security screening, in which case online check-in is restricted, and you must check in at the desk. After speaking with an Aer Lingus agent at the airport, they confirmed that my online check-in was blocked due to my ticket being linked to another airline’s system, even though the flight number was Aer Lingus. While it was a bit frustrating, the airport check-in process was smooth and handled by friendly staff. My advice to fellow travelers is to try online check-in early—it opens 48 hours before short-haul flights and 24 hours before long-haul flights—but if it doesn’t work, don’t panic. Just arrive at the airport early and go to the check-in desk. In summary, Aer Lingus may not allow online check-in for a number of reasons, including codeshare flights, document issues, special travel needs, or system limitations. It’s always good to check your booking details and reach out to Aer Lingus customer support if you’re unsure. Knowing these common issues can save time and reduce stress before your flight.