I completed the procedure no problem for my car, but could not repeat it for my wife's car.
The problem was on the Payment page where the card number and security code boxes were greyed out and could not be completed. I tried making changes, including re-starting Firefox, to no avail. I had to use Google Chrome to get the job done. This does point the finger at Firefox.
Firefox 128.0.2 (64bit) on Windows 10.
