Collecting survey feedback inside an existing Case record

We are using Case records for mentoring requests. Case generation happens via an API call. Upon case closure we're looking to send out an email invite to user with a link to a survey web form on our website. We have the survey response fields already created within a new Case tab in Creatio:

 

The problem is that we're not quite sure which endpoint to use to get the users' form submission data into the survey response. I've tried a GET to the case object but don't see these fields returned, raising questions about how to POST it correctly. Ideas?