Originally Posted by
DCEsquire
Wouldn't let me do it for a flight that I already fairlocked unfortunately. ....
Credit can not be used if the flight has a assigned PNR because the "new" will have the previous cancelled flight's PNR. So only for "new" flight bookings.
Originally Posted by
DCEsquire
... Do they mail me a cert or something?
the wiki has the step by step explanation. There a multiple caveats.