Send an application with a WebAPI

There is an online store on OpenCart 2.3

it has an application for calculation of cost of a product, now the application from the site comes to us in the mail, want to come into our CRM. WebAPI for interaction did accept a POST request in JSON format

Problem: the data of the application form in JSON and send the request to our WebAPI instead of mail. Code to generate JSON and sending does not have to be accessible from the outside.

The cost of the work offer