score:3
It seems the only thing that keeps you from paying by credit card is a fiscal code (codice fiscale). Very strictly speaking this code is assigned to you by the Italian tax authorities, but as a practical matter it is easily derived from your name and date and place of birth. Many websites offer this, e.g. this one does so for people born abroad (make sure to enter the Italian name of your country of birth). In rare cases when two people have the same codice fiscale, the code would need to be adjusted, but this should not be a concern to you as you state that you are also stating your case number and license plate.
Upvote:3
There is some (cryptical) reference or file number in the letter that you received (most probably on the top of the letter and doubled as bar code). Put that number into the transaction title.
(that was what I did and the fine was fine).