Qantas Flight Credit - Can You Even Redeem This through The Website?

I have flight credit due to a cancelled flight in 2020 which expires 31/12/23. I went to book with the same names but when you click Redeem - it takes you to an error page. It's been like this for the past 48 hours. You can't do it on Qantas checkout because you need a voucher number which does not come with credit. Has anyone else used flight credit before and is it meant to apply automatically?

UPDATE

FYI any old flight credit, even within the expiry date, still expires on the Qantas system well before that. Had to speak to them over the phone and they provided new codes.