I want to use a (substantial) future flight credit toward the purchase of a ticket from UA, on AC metal. UA is telling my travel agent that in order to use the FFC, I need to book a higher fare class than I want. I thought a future flight credit could be used toward the purchase of any published UA fare. Am I wrong about that? (The travel agent is trying to sort that out with their contacts at UA, but just wondering what your experience/knowledge is). Thanks.