Creates a new checkout context and redirects to the checkout website using details from the request body.

Sent from the user's browser via a form POST, will start a checkout session within Zip. It will automatically redirect the user to our Zip checkout. You need to ensure you provide your merchant ID, merchant reference (the unique ID you use for the order in your system), confirm/cancel URLs, and the order amount. The order amount should include all shipping, tax, and discount charges. You do not need to provide the order ID as that will be generated for you. Passing as much customer information as possible will improve the user experience by pre-filling data fields and improving conversion.