title: SecurityProtocolTypeExtensions.Tls12; does not exist in current context
body: <p>I am updating Security protocols to my existing 3.5 .net framework application  to work my payment gateways smooth.  I have added following code  </p>
  
  <pre><code>System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolTypeExtensions.Tls12;
  </code></pre>
  
  <p>in my <code>Global.asax</code> in <code>Application_Start</code> but it is giving me compile time error that  </p>
  
  <blockquote>
    <p>The name 'SecurityProtocolTypeExtensions' does not exist in the
    current context</p>
  </blockquote>
  
  <p>I was following this link S<a href="https://support.microsoft.com/en-us/help/3154517/support-for-tls-system-default-versions-included-in-the-.net-framework-2.0-sp2-on-windows-vista-sp2-and-server-2008-sp2" rel="nofollow noreferrer">upport for TLS System Default Versions included in the .NET Framework 3.5.1 on Windows 7 SP1 and Server 2008 R2 SP1</a> provided by Microsoft.</p>
  
  <p><strong>Update 1:</strong></p>
  
  <p>Also tried as told in above link, added both files in project, now I am getting an exception "<code>System.NotSupportedException</code>: The requested security protocol is not supported"</p>
  
  <p><strong>Updated 2:</strong> </p>
  
  <p>Tried as suggested by Jon Davies, but still no luck. same Exception <code>System.NotSupportedException</code></p>