Problem with creating datasource under gateway through API

Hi,
I am trying to create new datasources under gateway using api from C# but still gets error response "400: Bad request".

Supplied credentials encrypted as described in https://msdn.microsoft.com/en-us/library/mt784645.aspx

Here's code i'm using...

 string powerBIDatasourcesApiUrl = String.Format("https://api.powerbi.com/v1.0/myorg/gateways/{0}/datasources", gatewayId); 
 HttpWebRequest request = System.Net.WebRequest.Create(powerBIDatasourcesApiUrl) as System.Net.HttpWebRequest;
 //POST web request to create a datasource.
 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 datasourceJson =
                "{" +
                    "\"name\":\"" + <datasourceName> + "\"," +
                    "\"type\":\"Sql\"," +
                    "\"connectionDetails\":\"{\"server\":\"<server>\",\"database\":\"<database>\"}\"," +
                    "\"credentialDetails\":{" +
                        "\"credentials\":\"" + <credentialsHash> + "\"," +
                        "\"encryptionAlgorithm\":\"RSA-OAEP\"," +
                        "\"encryptedConnection\":\"Encrypted\"," +
                        "\"privacyLevel\":\"Public\"," +
                        "\"credentialType\":\"Windows\"" +
                    "}}";
//POST web request
 byte[] byteArray = System.Text.Encoding.UTF8.GetBytes(datasourceJson);
 request.ContentLength = byteArray.Length;

 //Write JSON byte[] into a Stream
 using (Stream writer = request.GetRequestStream())
 {
 writer.Write(byteArray, 0, byteArray.Length);
 writer.Flush();
 writer.Close();
 writer.Dispose();

 var response = (HttpWebResponse)request.GetResponse();

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