I've had a problem renewing my son's concession ticket (he's a student).
Renewed mine no probs but with his it wanted me to upload his ID, which I did, and then it fails when you go to pay, saying "Cart Not Found".
I've reported this to the ticket office, even taken screen recordings showing the problem, and I know it's affecting others who are trying to order season tickets where some sort of proof of concession is required, but the only advice I've been given is to go to the ticket office to do the renewal.
It's not a problem for me as I only live 10 mins away and am around during the day but strikes me it's affecting many other people so no idea why they aren't getting it fixed.