Completing an order with our Checkout API involves the following :
When orders are placed in your website.
Application server sends the checkout URL to your frontend,
you redirects the customer to the checkout page appears prepopulated with the transaction information.
The checkout UI performs data entry validation, such as verifying that all the required fields are populated and verifying that the card expiration date is valid.
Checkout pages are to be embed with a unique URL provided by us.

Checkout API is supported in the following countries:
Australia
Canada
United States
United Kingdom
Your hosting solution must be able to support dynamic pages with server-side scripting
(such as PHP, Ruby, ASP, and Java).
Applications that use OAuth need PAYMENTS_WRITE and ORDERS_WRITE permissions.