UpdateTask Error

Need to execute a function at a scheduled time, once only. So I create a task and at the end of the task function use UpdateTask API to disable this task by set active property to false. But UpdateTask API keeps return error:

{
  "code": 400,
  "status": "BadRequest",
  "error": "InvalidParams",
  "errorCode": 1000,
  "errorMessage": "Invalid input parameters",
  "errorDetails": {
    "Name": [
      "The Name field is required."
    ],
    "Identifier": [
      "The Identifier field is required."
    ]
  }
}

Here is Cloud Script code:

let url = "https://" + TITLE_ID + ".playfabapi.com/Admin/UpdateTask";
let method = "post";
let contentBody = JSON.stringify({
    Identifier: {Name: taskName},
    Name: taskName,
    Schedule: schedule,
    Parameter: {FunctionName: functionName, Argument: {}},
    Type: {CloudScript: functionName},
    IsActive: false
});
let contentType = "application/json";
let headers = {"X-SecretKey": X_SECRET_KEY};
let responseStr: string = http.request(url, method, contentBody, contentType, headers);

As the code shows Name & Identifier fields attached. The error message dosen't make sense to me. Any hint or suggestion? Thanks.

BTW, the DeleteTask & CreateTask APIs work great.