HTTP Status Code: NotFound

Hi, developers

i am authenticating my web server application using the code below in c#

string AppKey = "my app key";

string AppSecret = "my app secret key";

var Serverurl = @"https://platform.devtest.ringcentral.com/restapi/oauth/token";

string AppName = "FaxOutApp";

string AppVersion = "0.0.1";

SDK sdk = new SDK(Base64Encode(AppKey), Base64Encode(AppSecret), Serverurl, AppName, AppVersion);

string UserName = "16266718052";

string Extension = "101";

string Password = "my password";

var response = sdk.Platform.Login(UserName, Extension, Password, false);

here response throw an error of HTTP Status Code : Not Found

can any one help me for this.

any help will be appreciated.

Thanks