Using Flying Club miles to upgrade at the airport

Good Evening,
Newbie here to the V-flyer forum. Planning a forthcoming trip in a couple of months to the Caribbean to celebrate OH 40th B'day.
We both have enough miles to upgrade from Economy to PE, but upon calling the FC they have advised the dates I'm looking at does not have availablility to redeem miles for an upgrade.
I asked if there was space could I do it at the airport & they said yes, however after hanging up I forgot to ask about the booking class.
So normal conditions are that you book a ticket in L class or above to redeem miles. There are cheaper fares available in O class and I forgot to ask if there is an exception at the airport as to whether you can redeem miles even if booked in a lower booking class or if it is a strict No.
Any advice would be greatly appreciated.
Thanks in advance
Clade
Newbie here to the V-flyer forum. Planning a forthcoming trip in a couple of months to the Caribbean to celebrate OH 40th B'day.
We both have enough miles to upgrade from Economy to PE, but upon calling the FC they have advised the dates I'm looking at does not have availablility to redeem miles for an upgrade.
I asked if there was space could I do it at the airport & they said yes, however after hanging up I forgot to ask about the booking class.
So normal conditions are that you book a ticket in L class or above to redeem miles. There are cheaper fares available in O class and I forgot to ask if there is an exception at the airport as to whether you can redeem miles even if booked in a lower booking class or if it is a strict No.
Any advice would be greatly appreciated.
Thanks in advance
Clade