Originally Posted by
davidj1
Interesting. So their system somehow knows who has a visa and denies check-in unless visa has been approved?
Even more interesting they let you arrive at the airport without telling you they're about to deny you boarding

The system doesn't know who has a visa. It knows the passport which the guest is travelling on & knows that a visa is required for the destination. It then stops online checkin, because a manual check of that visa is required by staff at the airport. If online checkin proceeded, the guest could get as far as the gate or possibly onboard the plane without a visa check.
It is the guests responsibility to know a visa is required for a destination. Not the airline.