This endpoint is used to send form submission data to HubSpot, including those using AJAX. Form submissions from external sources can be made to any registered HubSpot form. You can see a list of forms on your account by navigating to Marketing > Lead Capture > Forms.
We recommend creating a unique form in HubSpot to parallel your custom website form. This will make it easy to track submissions on that particular custom form in the future.
x-www-form-urlencodedendpoint? You can find the details for that endpoint here.