If online check-in is unavailable, you are not necessarily in trouble, but you must shift your strategy to an airport-based check-in. This situation often occurs due to technical glitches, the need for manual document verification (common on international routes with complex visa requirements), or because the airline has "flagged" your reservation for a random security check (such as the "SSSS" code in the U.S.). In these cases, you should arrive at the airport significantly earlier—typically three hours before an international flight and two hours for domestic—to visit the physical check-in counter. The ground staff will verify your passport, visas, or health documents and issue a physical boarding pass. Most airlines do not charge an extra fee for airport check-in if the online system was verifiably down, but "low-cost" carriers may still try to enforce fees unless you can prove the technical error. Always have your booking reference number and digital confirmation ready to expedite the process at the desk.