Getting an HTTP 429 error while accessing BOX API

{"error":"temporarily_unavailable","error_description":"The server is currently unable to handle the request due to a temporary overloading of the server"}

Here is the call to get token:

    _getToken: function () {
            var that = this;
            var settings = {
                "async": true,
                "crossDomain": true,
                "url": "https://api.box.com/oauth2/token",
                "method": "POST",
                "headers": {
                    "content-type": "application/x-www-form-urlencoded",
                    "cache-control": "no-cache"
                },
                "data": {
                    "grant_type": "client_credentials",
                    "client_id": this._box_client_id,
                    "client_secret": this._box_client_secret,
                    "box_subject_type": "enterprise",
                    "box_subject_id": this._box_subject_id
                }
            }
            $.ajax(settings).done(function (response) {
                console.log(response);
                that._token = response.access_token;
                that._getFilesFromBox(response.access_token)
            });
        },