Browsing to the domain you mentioned, I was redirected to a site hosted at a numeric IP, which would explain the problem. The cart must set a cookie in the buyer's browser to keep track of which cart instance is theirs; however, cookies must be set for a specific domain, and cannot be set for a numeric IP. Therefore, the cart on that site "forgets" anything added to it as soon as the buyer closes their cart display. You will need to get the site accessible via some domain name to get the cart fully functional.
This help page covers the topic in more detail, including some tips you may find useful if you need to set up a subdomain on shared hosting for development/testing before you can get the bftix.org domain resolving to the site directly: