public string GetSessionID()
    {
        string callname = "GetSessionID";

        #region Initialise Needed Variables

        //Get the Server to use (Sandbox or Production)
        string serverUrl = ConfigurationManager.AppSettings["TradingService"];

        //SiteID = 0  (US) - UK = 3, Canada = 2, Australia = 15, ....
        //string siteID = "0";

        eBayAPIInterfaceService service = new eBayAPIInterfaceService();
        string requestURL = serverUrl + "?callname=" + callname + "&siteid=" + siteID
                            + "&appid=" + AppID + "&version=" + version + "&routing=default";
        service.Url = requestURL;

        // Set credentials
        service.RequesterCredentials = new CustomSecurityHeaderType();
        service.RequesterCredentials.Credentials = new UserIdPasswordType();
        service.RequesterCredentials.Credentials.AppId = AppID;
        service.RequesterCredentials.Credentials.DevId = DevID;
        service.RequesterCredentials.Credentials.AuthCert = CertID;
        #endregion

        GetSessionIDRequestType request = new GetSessionIDRequestType();
        request.RuName = ConfigurationManager.AppSettings["RuName"];
        request.Version = version;
        GetSessionIDResponseType response = service.GetSessionID(request);
        return response.SessionID;
    }