Form Submission With Unique Key Not Autoincrement

Hi,

I have a form in which I added a Unique key.

I have a requirement to submit the form from jotform API 
https://api.jotform.com/docs/

I am using POST "https://api.jotform.com/form/{formID}/submissions?apiKey={apiKey}"

But the issue I am facing when submitting the form from API the unique key field is not auto increment how to achieve that ?

Thanks
Vishal