Retailers on Loopt Star pay the company an undisclosed fee for every visit the app gives them.

FORBES: Loopt Star Launches As A Virtual Loyalty Card

For example, the US requires Argentine, Chilean, Bolivian, Brazilian and Paraguayan nationals to pay a fee to visit the US, and in turn, those countries levy a charge on US travellers to their countries.

BBC: New fees for visiting South America

But the others refused, resulting in longer stays and higher costs (and a fee for every visit, while the better group happened to be the only salaried one).

NEWYORKER: The Hot Spotters

But Russians still need a stamp in their passports and must pay a fee (although residents of the Kaliningrad exclave have secured special arrangements to visit Poland).

ECONOMIST: Visas in Europe