I have to mention that I have asked and my cousin has asked about how to upgrade on flex pay. (I asked for her when I thought she had the wrong understanding.) They didn't realize how much they would love Uni and how much parking would add up). We both asked in person and no one has ever mentioned a fee.
I'm not sure who mentioned a fee to you, Damo!
(I also asked here and was told that we'd been given the right info and I don't remember being told about a fee here)