There are several reasons why Aer Lingus might not allow you to check in online, and understanding these can help you avoid frustration and delays. The simple difference often comes down to specific travel conditions, booking details, or airline policies. One common reason is if you are traveling with infants or require special assistance. In such cases, Aer Lingus needs to ensure proper support and safety checks, which means online check-in is disabled, and you must check in at the airport. Another reason relates to international travel requirements. If your flight involves countries with strict visa or entry regulations, Aer Lingus may require you to present and verify your travel documents in person before boarding. This means online check-in is not available until those checks are completed. Additionally, if your flight is a codeshare operated by another airline, online check-in might be restricted because the operating airline controls the check-in process. In this case, you may need to check in directly with the partner airline. Technical or booking issues can also prevent online check-in. Missing or incorrect passenger details like passport information, or problems with your booking reference can cause the system to block online check-in. Ensuring your booking is complete and accurate usually resolves this problem. Some fare types, such as group bookings or special discounted tickets, may have limited online check-in availability. Airlines sometimes require these passengers to check in at the airport for added verification. Timing also matters—Aer Lingus opens online check-in usually 36 hours before departure and closes it about 90 minutes before the flight. Trying to check in too early or too late will result in no online check-in option. Overall, the simple difference between being able to check in online or not usually depends on travel requirements, passenger needs, booking type, or timing. When online check-in is not available, arriving early at the airport and using the check-in counters is necessary. Preparing your documents ahead of time and verifying your booking details can help avoid issues. If you’re unsure why online check-in is blocked for your flight, contacting Aer Lingus customer service will provide clarity and guidance. Understanding these reasons allows you to plan better and have a smoother start to your journey with Aer Lingus.