IIS Proxy Settings for ASP.Net Core

Question

I have IIS (10.0) on Windows Server 2019 (v.1809) and a few asp net core applications. And I have corporate proxy. The problem is that applications can't go pass it:

System.Net.Http.HttpRequestException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

Or in some other sites:

System.Net.Http.HttpRequestException: No connection could be made because the target machine actively refused it.

From browsers (IE, Chrome) links work. Another server with IIS, same applications and same proxy settings works fine too.

I tried to set proxy settings specifically in config files, but it didn't help. From here: How to set proxy settings for IIS processes?

What else can I do?

Edit: I created ASP Net Framework web-app and run it on the same server. Witout proxy it didn't work, but with proxy in web.config (in site folder or in Microsoft.NET folder) it worked. For Core I still have not found a solution.

Code is the same in ASP Net and ASP Net Core:

    public async Task<IActionResult> Index()
    {
        using (var client = new HttpClient())
        {
            try
            {
                var message = await client.GetStringAsync("http://webcode.me");
                ViewBag.Message = message;
            }
            catch (Exception ex)
            {
                ViewBag.Message = ex.ToString();
            }
         }
         return View();
     }

Answer 1

After so many tries to overcome proxy in the end it was problem with organization network settings. Resolved with technical support help.