Originally Posted by
gooselee
Welcome to FT!
Delta changed the rules for GUCs (and RUCs) early last year. They can now be used on Pay With Miles tickets (as well as Amex companion tickets and I think SkyBonus which were all previously not allowed). The agent you spoke to was reciting old rules, and your best bet is just to call again and talk to a different agent. Ask for a supervisor if you need to.
I have a skybonus ticket reserve for my co worker in February, and have apply an GUC on it, but later an agent contact me, to advise me GUC can not be apply on Skybonus ticket.