Convert variable that contain string data into JSON Object for JavaScript REST API

Question

Here I have variable named item and contain following data:

{
  __metadata: {
    "type": "SP.Data.ClinicalTestingPhaseIIListItem"
  },
  Control: 1,
  Randomization: 2,
  Blindings: 3,
  Groups: 4,
  DoseTitration: 5,
  Stratification: 6,
  PatientsDoseLevel: 7,
  TumourResponse: 8,
  DetermineWarrants: 9,
  Title: 1
}

Now when I pass it to my ajax call written below that gives me a error after some research I get conclusion that the data passed in string format instead of object.

Microsoft.SharePoint.Client.InvalidClientQueryException: A node of type PrimitiveValue was read from the JSON reader when trying to read the start of an entry. A StartObject node was expected.

Below is my ajax call

jQuery.ajax({
        url: requestUri,
        type: "POST",
        data: JSON.stringify(item),
        headers: header,
        success:function(){
        alert("List itme Inserted Sucessfully");    
        },
        error: function(data){
        console.log(data);
                alert(data.responseText);
        alert("Error Occured");
        }
});

Answer 1

Remove JSON.stringify and see

jQuery.ajax({

        url: requestUri,
        type: "POST",
        data: item,
        headers: header,
        success:function(){
        alert("List itme Inserted Sucessfully");    
        },
        error: function(data){
        console.log(data);
                alert(data.responseText);
        alert("Error Occured");
        }
});