The BillAgain Application Programming Interface (API) is a set of services offered by BillAgain which allow external applications (websites, apps or any software) to interact and interface with BillAgain in order to make use of BillAgain without physically logging in to BillAgain. This allows developers to bill their users using BillAgain for goods or services offered to them, saving them development time and providing them with a simplified and convenient way to manage billing. Allowing developers to focus on their application whilst BillAgain securely handles billing for them. This eradicates the headache of PCI Compliance for developers, since BillAgain provides secure PCI Compliant credit card storage and facilitates payments securely over encrypted HTTPS connections.