Which payment method is restricted to the U.S.?

ApplePay is primarily designed for use in the United States, particularly because it integrates tightly with the U.S. banking system and credit card networks. While it has gained traction in other countries, its features, acceptance by merchants, and overall functionality are most robust in the U.S. market. For instance, many retailers in the U.S. have adopted ApplePay as a standard payment option due to its convenience and security features, making it more prevalent compared to its use in other countries.

Other payment methods mentioned have broader international applications. PayPal operates globally, allowing users to send and receive money in many countries. Square, while focused on small to medium businesses in the U.S., is expanding internationally as well. Nochex is a payment processor that is popular mainly in the UK, emphasizing its limitations outside the U.S. Thus, the positioning of ApplePay predominantly within the United States highlights why it is the correct answer in this case.