HttpClient - throwing connection refused when using Https
If you make a simple HTTS request using HttpClient and you get an exception message saying "connection has been refused by remote host", then most likely is you're using .Net 4.5 or below which does not support HTTPS request.
Upgrade your project to .Net 4.6 and you're good.
Updates :- In case you still facing the issue in your Web Project like ASP.Net MVC, please try adding the following code before you make a https request :
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
Here's a sample implementation code :