"One way to know if your country is allowed or not is to open https://nitrogensports.eu/ on your browser and if the country is restricted it will give you an "Error 1009 Access denied" message. So if you are living in USA, just open the site and see if its lets you in or not.
Secondly, i have searched the terms and condition page (https://nitrogensports.eu/n/terms) but i did not find any such information regarding banned countries by nitrogen sports."

My partner placed many bets from Costa Rica, with a CR IP. So I don't think this works. CR isn't mentioned in their TC. Have you ever seen a country blocked by this?