Single textual message to one destination C#

var client = new RestClient("http://api.metrotel.com.bd/sms/2/text/single");

var request = new RestRequest(Method.POST);
request.AddHeader("accept", "application/json");
request.AddHeader("content-type", "application/json");
request.AddHeader("authorization", "Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==");
request.AddParameter("application/json", "{\"from\":\"8809612316267\", \"to\":\"8801786739367\",\"text\":\"Test SMS.\"}", ParameterType.RequestBody);

IRestResponse response = client.Execute(request);

// Here QWxhZGRpbjpvcGVuIHNlc2FtZQ== resemble base_64 encode of username:password