I can not post Yammer via Rest API using Ajax

Hi I would like to Create JavaScript app which post message to Yammer, using Yammer REST API. but I have a limitation. I Can Not use Yammer SDK to post message. so, I written code of ajax.

However, In this code Doesn't work. XMLHTTPrequest is always "access denied".

why this code doesn't work?

MY Yammer network allow 3rd party app.

function sendData() {

    var messagebody = new Object();
    messagebody.body = "This is test";
    messagebody.group_id ="4627253"
    
    //get accToken 
    accToken = responseObject.access_token.token;
    var accAuthHead = "Bearer "+ accToken;

    $.ajax({
        url: "http://ift.tt/1pm9iTE",
        type: 'POST',
        headers: {
            'Accept': 'application/json, text/javascript, */*; q=0.01',
            'Accept-Encoding': 'gzip, deflate',
            'Authorization': accAuthHead.toString(),
            'X-Requested-With': 'XMLHttpRequest',
        },

        data: JSON.stringify(messagebody),
        datatype: "json",

        success: function (data) {
            console.log("ajax post success.");
        },
        error: function (XMLHttpRequest, textStatus, errorThrown) {
            alert("There was an error with the request." + textStatus.toString()+ XMLHttpRequest.toString());
        }
    });


}