var client = new RestClient("https://www.waboxapp.com/api/send/chat");
var request = new RestRequest(Method.POST);
request.AddHeader("content-type", "application/x-www-form-urlencoded");
request.AddParameter("application/x-www-form-urlencoded", "token=my-test-api-key&uid=12025550123&to=12025550193&custom_uid=msg-3893&text=Hello+world%21", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);