If you need shopping cart functionality, please check our Shopping Cart REST API
It supports the full checkout process, and it creates an order at the end of the process.
Shopping Cart REST API demo:
http://api.opencart-api.com/demo/shopping-cart/
If you need administration functions, stock management, product management, etc, please check our
REST ADMIN API
REST ADMIN API demo:
http://api.opencart-api.com/demo/admin/