Complex sentence: Passengers with e-tickets are required to check-in at the airport for a flight in the usual manner, except that they may be required to present an e-ticket itinerary receipt or personal identification, such as a passport, or credit card.
Split into simpler sentences: Passengers with e-tickets are required to check-in at the airport for a flight in the usual manner. They may be required to present an e-ticket itinerary receipt or personal identification, such as a passport, or credit card.