Each integrated Two Tap store belongs to a country. For instance, a US integrated store will only accept US shipping/billing information.
International partners working with the Two Tap API send products to US fulfillment centers they control and ship the products overseas using their own logistics solutions.
Two Tap has limited built-in crossborder functionality. To find out more about this consult the API docs: https://docs.twotap.com/docs/api-international-crossborder.