Rest Api: search in post request

i’m trying to use the rest api service to search inside an entity but i receive a 500 error when i try to do this request by javascript after the authentication. In catalina i see this error : Expected BEGIN_OBJECT but was STRING at line 1 column 1 path.
Sorry Can someone help me to find the error?

function loadTrace() {
    var d={
                  "property": "booleanField",
                  "operator": "=",
                  "value": true
        "view": "someViewName",
        "returnCount": true
        url: 'http://localhost:8080/app/rest/v2/entities/trace_Tracciabilita/search',
        headers: {
            'Authorization': 'Bearer ' + oauthToken,
            'Content-Type': 'application/x-www-form-urlencoded'
        dataType: 'json',
        success: function (data) {
            $.each(data, function (i, tracciabilita) {
                $('#customersList').append("<li>" + tracciabilita.id_soggetto.denominazione + " ( )</li>");


In the documentation there are two examples of searching with filter:

One of example requests uses “conditions” json object.
Another - “filter” - “conditions” json objects.

The request body you send doesn’t look like any of them.