For a scheme of work without using 3-D Secure, there are automatic interactions between the store systems and the payment gateway:

• 2, 3
• 6, 8

For the scheme of work using 3-D Secure, there are automatic interactions between the store systems and the payment gateway:

• 2, 3
• 6, 9
• 14, 16

These interactions are synchronous, i.e. the caller must wait for a response or timeout to continue working, and also unidirectional – the store system always contacts the payment gateway and never vice versa. To enable the store system developer to implement these interactions, the payment gateway system exposes an API from the following requests:

1. Register order
2. Pay/pre-authorize an order
3. Authorize an order