How do I purchase an additional Baggage Option? When purchasing your ticket online Any time after purchasing your ticket and up to 30 hours before your flight’s departure, in the Your Reservations area During online check-in, for departures from most airports and for flights provided on Air France aircraft https://www.airfrance.us/US/en/common/resainfovol/services/achat_franchise_bagages.htm#additional-baggage-option
When purchasing your ticket online
Any time after purchasing your ticket and up to 30 hours before your flight’s departure, in the Your Reservations area
During online check-in, for departures from most airports and for flights provided on Air France aircraft
https://www.airfrance.us/US/en/common/resainfovol/services/achat_franchise_bagages.htm#additional-baggage-option