Referral domain doesn't work in ASP.NET Webforms application

Question

I have an old website developed in ASP.NET Webforms, I need to make changes to the main page where I have to check the referral domain name..

If referral domain name is abc1.com, abc2.com or abc3.com, then I have to redirect to a different page.

I tried the following code but none works.

Code #1 example

    Uri myUri = Request.UrlReferrer;

    if (myUri != null)
    {
        Response.Write("myUri.Host" + myUri.Host);
        //Response.Redirect("https://www.example.com/page1?referal=" + myUri.Host, true);
    }

Above example is not working as it always return null

Code #2 example

Since above code is not full proof, I tried to read the header information

    NameValueCollection headers = base.Request.Headers;

    for (int i = 0; i < headers.Count; i++)
    {
        string key = headers.GetKey(i);
        string value = headers.Get(i);
        base.Response.Write(key + " = " + value + "<br/>");
    }

Values returned by above code doesn't show any correct referral domain as it always shows the main domain of the website under host Host = www.example.com | x-sp-edge-host = www.example.com | x-fb-host = www.example.com and not the referral domain.

Besides this, I also tried combination of different code with no success.

Any pointer where I could be going wrong.

I used inspect tool to dig further and it always show the referral domain from 3 domain but code is not able to trap it

Screenshot for your reference:

**CODE EXAMPLE in Page_LoadEvent **

if (!IsPostBack)
        {
            Response.Write("*** !IsPostBack<br><br>");
            string requestedDomain = HttpContext.Current.Request.ServerVariables["HTTP_HOST"];
            Response.Write("requestedDomain HTTP_HOST" + requestedDomain);
            Response.Write("<br> HTTP_REFERER" + HttpContext.Current.Request.ServerVariables["HTTP_REFERER"]);
            Response.Write("<br> ALL_HTTP" + HttpContext.Current.Request.ServerVariables["ALL_HTTP"]);

            Uri myUri = Request.UrlReferrer;

            if (myUri != null)
            {
                Response.Write(Request.UrlReferrer.ToString());
            }
            else
            {
                Response.Write("****Request.UrlReferrer.ToString()<br><br>");
                Response.Write("NULL");
                Response.Write("****Request.UrlReferrer.ToString()<br><br>");
            }

            NameValueCollection headers = base.Request.Headers;
            for (int i = 0; i < headers.Count; i++)
            {
                string key = headers.GetKey(i);
                string value = headers.Get(i);
                base.Response.Write(key + " = " + value + "<br/>");
            }
        }

This code always show main domain in header information and not the referral domain. while when i check using inspect tool in browser it show referral domain as shown in screenshot above as first entry.