Web API - 无法连接到远程服务器

如何解决Web API - 无法连接到远程服务器

当我们尝试从应用程序获取访问令牌时，它抛出以下错误。不确定是否必须使用代理或任何其他方法来获取访问令牌。

public object GetToken()
    {
        RestSharp.Deserializers.XmlDeserializer deserial = new RestSharp.Deserializers.XmlDeserializer();
        var client = new RestClient("https://apis-stage.iocn.com/v1/auth/token");
        var request = new RestRequest(Method.POST);
        request.AddHeader("cache-control","no-cache");
        request.AddHeader("content-type","application/json");
        request.RequestFormat = DataFormat.Json;
        request.AddHeader("authorization","client_id:xxxxx-7b14-xxx-xxx-xxx,client_secret:xxxxxv.xxxx-Z_xx4Ir");
        request.AddParameter("application/json","{\n\"grant_type\":\"client_credentials\"\n}",ParameterType.RequestBody);
        IRestResponse response = client.Execute(request);
        var returnData = deserial.Deserialize<object>(response);
        return returnData;
        //if (returnData.data[0].access_token != null)
        //{
        //    access = returnData.data[0].access_token; //This correctly gets the Access Token.
        //}

        //request.AddHeader("authorization","Bearer <access_token>");
    }

错误

无法连接到远程服务器连接尝试失败，因为连接方在一段时间后没有正确响应，或建立连接失败，因为连接的主机未能响应 15.237.145.121:443