Is that possible to send HttpWebRequest using TLS1.2 on .NET 4.0 framework

Question

Yes, it supports it but you must explicitly set the TLS version on the ServicePointManager. Just have this code run anytime (in same app domain) before you make the call to Experian:

System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12

Update

see @iignatov 's answer for what you must do for framework v4.0. My code works with 4.5+

I had to deal with the same problem, while integrating PayPal into a legacy application, and found the following workaround for .NET 4.0 which seems to do the trick:

ServicePointManager.Expect100Continue = true;
ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
ServicePointManager.DefaultConnectionLimit = 9999;

Basically the workaround is to directly assign the port for TLS 1.2.

All credit goes to the commenter at CodeProject.

The VB.NET Translation of iignatov's answer:

ServicePointManager.Expect100Continue = True
ServicePointManager.SecurityProtocol = CType(3072, SecurityProtocolType)
ServicePointManager.DefaultConnectionLimit = 9999

I was solved with this way.

    string url = "https://api.foursquare.com/v2/blablabla...";
    var request = (HttpWebRequest)WebRequest.Create(url);

    ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
    
    var response = (HttpWebResponse)request.GetResponse();
    var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

You can also use this:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | (SecurityProtocolType)768 | (SecurityProtocolType)3072;