US, Sept. 16 -- A passenger arrives at the airport with a valid passport, a confirmed ticket and an eVisa. But how does the airline know that the eVisa is authentic?

It's an important question. Before a passenger can board an international flight, the airline must confirm that they hold the documents required to enter their destination country. Get it wrong, and the airline can face fines and removal costs averaging USD 9,000 per passenger.

And the answer to how airlines verify eVisas might surprise you.

While travelers benefit from the simplicity of eVisa issuance, airlines face the complexity of verifying them.

Proof that an eVisa has been issued might take the form of an email, a PDF or a QR code. Verification might require a websi...