Hi,
Please try and change your code from:
client_ = new RestClient(url);
client_.Authenticator = new HttpBasicAuthenticator("admin", "admin");
RestRequest request = new RestRequest("tag/add", Method.POST);
request.AddHeader("Content-Type", "application/json");
request.RequestFormat = DataFormat.Json;
request.AddBody("hello");
client_.Execute(request);
To:
var client_ = new RestClient(url);
client_.Authenticator = new HttpBasicAuthenticator("admin", "admin");
RestRequest request = new RestRequest("tag/add", Method.POST);
request.AddHeader("Content-Type", "text/plain");
request.AddBody("hello");
client_.Execute(request);
Another option is in your receiving Web API/Service is to use Newtonsoft to de-serialize the input parameter into a string.
For example:
public string TagAddWebService(string bodyInput)
{
string value = Newtonsoft.Json.JsonConvert.Deserailize<string>(bodyInput);
}</string>