I called them with an issue, and they agreed to send me an express replacement. To complete the request, they sent me a link that I had to visit to enter my payment details so they could put a hold on my card for the replacement device. Unfortunately, everytime I tried to do this, I had the same problem you’re seeing.
The only way Apple were able to solve this was to setup the repair request for me by taking my payment details over the phone, and inputting them straight into their system.
Give them a call and explain what’s happening......they should be able to do the same for you.