Netsuite insert phoneCall to supportcase not working

Question

I want to add a phonecall to one of my supportcases.
When I use the following request, I get an error.

POST https://[CN].suitetalk.api.netsuite.com/services/rest/record/v1/phoneCall

The body:

{
  "title":"test",
  "message": "test call",
  "phone": "+3101234567",
  "supportcase": 555
} 

The error:

{
    "type": "https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.1",
    "title": "Bad Request",
    "status": 400,
    "o:errorDetails": [
        {
            "detail": "Error while accessing a resource. You have entered an Invalid Field Value 555 for the following field: supportcase.",
            "o:errorCode": "USER_ERROR"
        }
    ]
}

The documentation isn't clear enough, does someone know what I should use as value for the supportCase property?
I tried the caseNumber and also the internal ID.
Documentation: https://system.netsuite.com/help/helpcenter/en_US/APIs/REST_API_Browser/record/v1/2021.2/index.html#/definitions/phoneCall

Answer 1

When I try to add the related company as well, it works.

{
  "title":"test 12",
  "message": "test note",
  "phone": "+31642937986",
  "supportCase": 555,
  "company": 12
} 

The property company has to be send too, also the supportCase should be linked to that company for it to work

I had to use both internal Id's

Answer 2

supportCase is an object with its own definition - a 'nested property' if you will. Try:

{
    "title":"test",
    "message": "test call",
    "phone": "+3101234567",
    "supportcase": {
        "caseNumber": 555
    }
}