I am using LOT airline. I managed to check in on the airline's website from Warsaw to Dubrovnik, but not the other way around.
This flight is not supported.
LOT's website has a hint: If you were able to log into the check-in panel, but did not receive your boarding pass, check-in at the airport.
Website of Dubrovnik can't find my ticket.
Does it mean that I should be ready to pay for check-in at the airport?