QuestionnaireResponse on the FHIR specification website.

A structured set of questions and their answers. The questions are ordered and grouped into coherent subsets, corresponding to the structure of the grouping of the questionnaire being responded to.

The body should be a valid FHIR object for QuestionnaireResponse.

For example, if updating a Slot resource, here is a valid object:

{
  "resourceType": "Slot",
  "schedule": {
    "reference": "schedule/a"
  },
  "status": "free",
  "start": "2022-08-10T11:00:00Z",
  "end": "2022-08-10T12:00:00Z"
}

You can reference the FHIR documentation to determine the format for QuestionnaireResponse.