Fiscal code requested for online ticket buying

Are you on the English version of ticketone? Or you are using the Google Translated version of the site?
If you are using the English version of Ticketone, select any country different from Italy from the drop-down menu and the site will do what's written under the Fiscal code box:

If you reside in a country other than Italy and you are not in possession of a tax code, select the correct country and the code EE1 will appear in the form. It will not be necessary to insert any other code.

I don't know what the country list looks like on Ticketone.it, but if the US is listed there, it may appear as either Stati Uniti or Gli Stati Uniti.