Current State:

If your Request Forms doesn't contain any fields. Summary is hidden with default value and all other required fields are within the JSM Forms. Then creating a request with following payload:

{
"form": {
"answers": {
"1": {"choices": ["10001"]},
"2": {"choices": ["10005"]}
}
},
 "requestTypeId": "23",
"serviceDeskId": "2"
}

it fails with generic message:

This request is invalid. Check that the request contains all the required parameters and that the parameters are valid..

Here requestFieldValues parameter is always needed.

So correct payload would be:

{
"form": {
"answers": {
"1": {"choices": ["10001"]},
"2": {"choices": ["10005"]}
}
},
  "requestFieldValues": {
  },
 "requestTypeId": "23",
"serviceDeskId": "2"
}

Proposed Future State:

Provide better error messages indication which field or parameter is missing.

Alternative (e.g. Third Party Plugin):

xx