Discover and American Express are closed loop systems that may have marketing partnerships with banks but they actually issue the cards themselves and operator

Discover and American Express are closed loop systems that may have marketing partnerships with banks but they actually issue the cards themselves and operator their own networks. As a result, the American Express API is actually decent[0]. [0]: https://gateway-na.americanexpress.com/api/documentation/integrationGuidelines/index.html?locale=en_US https://gateway-na.americanexpress.com/api/documentation/int...