Interail self-service check out process

I am trying to make seat reservations for my trip in Italy.  I have already gotten a ticket on the rail planner app.  I click on the check out, and it wants me to put in Billing information in the site.   I cannot get past the Country section because it doesn’t have United States as a listed County. 

BTW it would be simpler if you could do this all within one app.  Very confusing.