Unable to update connection string using SetAllConnections API

Dear Techies,

I was successfully able to upload PBIX files to PBI Service using Import API. Now, I am trying to update the connection string using SetAllConnections API. The dataset that I am trying to update is using SQL Server as source and DirectQuery mode

Below is my query snippet, I am getting 404 bad request error

private static void UpdateConnection(string DatasetID)

        {

            string powerBIDatasetsApiUrl =String.Format("https://api.powerbi.com/v1.0/myorg/myorg/datasets/{0}/Default.SetAllConnections",DatasetID);

            HttpWebRequest request = System.Net.WebRequest.Create(powerBIDatasetsApiUrl) asSystem.Net.HttpWebRequest;

            request.KeepAlive = true;

            request.Method = "POST";

            request.ContentLength = 0;

            request.ContentType = "application/json";

            //Add token to the request header

            request.Headers.Add("Authorization", String.Format("Bearer {0}", token));

            string updateJSON = "{\"connectionString\":\"data source=XXXXX;initial catalog=XXXXX;persist security info=True;encrypt=True;trustservercertificate=False\"}";

            //POST web request

            byte[] byteArray = System.Text.Encoding.UTF8.GetBytes(updateJSON);

            request.ContentLength = byteArray.Length;

            //Write JSON byte[] into a Stream

            using (Stream writer = request.GetRequestStream())

            {

                writer.Write(byteArray, 0, byteArray.Length);

                var response = (HttpWebResponse)request.GetResponse(); ----Error at this line

                //Console.WriteLine(string.Format("Dataset {0}", response.StatusCode.ToString()));

                Console.ReadLine();

            }

        }

Am I missing something? Please help

Thanks,

Latheesh