What should I do if I have not been able to check in before closure of the flight?

You must respect the Registration Deadline. Otherwise, you are considered as not having shown up for check-in ("no show") and you will be refused to get on board (and if applicable, the return flight from your trip will be canceled through the defined conditions, in article 1.5.2 of these general conditions of sale and transport).

If you showed up after the flight closed, we recommend that you go to our Corsair counter as soon as possible to have our sales staff accept this status. They will do their utmost to find a solution on the next flight.
Please note: fees will apply.

If you do not go to our sales counter right after the flight closes, your ticket will be permanently and automatically canceled and will no longer be usable.