LNAT voucher invalid

I paid for the LNAT registration voucher a few days ago and recieved the code in my email. Today, I sat down to enter the code and book a test appointment, however, when I entered the code in the Voucher slot, the website said it was "Invalid" and "Had been used once". I don't get this because I didn't share the code with anyone and this is the first time I'm entering it in the slot, I haven't typed it anywhere before?. This is really making me worry because I'm already anxious about the test and this might delay my appointment. I sent an email to the LNAT voucher team, really hoping I get a reply soon. Has this happened to anyone? Should I be worried?

It may just be a technical issue as booking only opened a few days ago. They may still be processing things and the system is probably quite slow. I had no difficulty with my voucher but I wouldn’t worry about it for now. They will contact you once they have more information.