Calendly API How to add custom fields outside the widget?

Is it possible to include any custom fields like the one in the image in the Calendly form request that will display them in the body of the emails that the client and site owner receive?

I read in the documentation about new fields, and questions that come with iframe But this is not quite it. My task is to add my own fields when sending the form. Is it posiable in some JS code ?