This creates a Yelp Checkout Order and is to be called after the user builds and submits his/her order on the iframe. This call returns a yelp_order_id.

In other words, the iframe POST goes to the Partner server, where the user's request can be processed however necessary by the Partner. Immediately following this, the Partner must POST to the above URL to communicate to Yelp the details of the Order. In return, Yelp will give the Partner a yelp_order_id.

See Order resource for more info.