The request was aborted: Could not create SSL/TLS secure channel

 

// using System.Net;

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

// Use SecurityProtocolType.Ssl3 if needed for compatibility reasons

Note:

i.    Needed for .Net 4.5 because Tls12 is not a default protocol.

ii.   Need to write the above code only once within the application. (For example within 

      Global.asax > Application_Start within Web application or equivalent in Winforms application) 

iii.    For .Net 4.6 and above, Tls12 is a default protocol so it is not needed