I stopped traveling for a little over a month this year and when I returned the FCM system had completely changed. I am a little confused as to how this system works with electronic vouchers. If there's already been threads on this, feel free to link - I couldn't find any upon an initial search.

I travel for work and my company requires us to only book main cabin. Two weeks ago I had to fly out to LAX and decided it was worth the cost to purchase the FC upgrade ahead of time as I wanted to be as relaxed as possible (I knew it was going to be a stressful trip). DL.com wasn't working so I called the PM line and asked if I could possibly use my $800-about-to-expire digital voucher to pay for the FCM. They said yes and the FC upgrades for all my flights on this trip cost a total of $456. I was issued a new voucher for the remaining amount leftover. I was surprised to find that instead of getting a ticket with an upgrade fare of R, it was as an A fare and I did get the bonus MQMs, which you didn't get with the old FCM system when you bought a FC upgrade at check-in.

I was told that if there were no more K fares available on the trip (my original ticket fare) then I wouldn't be able to use the voucher to pay for the FCM offer. It sounded like because when applying the voucher, the system looks at an available coach fare on that flight and then applies the FCM, so if there are no more seats left at your original ticket fare, you can't use a voucher and instead must use a credit card. Does anyone know if this is the case or if I'm understanding this correctly?