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

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

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Reason: The error is generic and there are many reasons why the SSL/TLS negotiation may fail. The most common is an invalid or expired server certificate, and you took care of that by providing your own server certificate validation hook, but is not necessarily the only reason. The server may require mutual authentication, it may be configured with a suites of ciphers not supported by your client, it may have a time drift too big for the handshake to succeed and many more reasons.

Solution: Added some more code to make it works -

ServicePointManager.Expect100Continue = true;
ServicePointManager.DefaultConnectionLimit = 9999;
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12 | SecurityProtocolType.Ssl3;