Hi Rajkumar,
1) What return value can you see if call HttpClient.GetResponseStatusCode() after getting -1? 
Please try to see whether you can workaround this by setting httpClient.anonymousAccess = true, refer to AnonymousAccess - - Objects and Controls (appeon.com)
2) If your OS is Win 10, you can also set httpClient.SecureProtocol to 5 (TLS 1.2) and try again.
If still not resolved, Kindly please report your case via our support ticketing system to ensure it is being properly received by our tech support and tracked at: https://www.appeon.com/standardsupport/

Regards, Logan

Hi Rajkumar ;

  I would first suggest using a utility like Postman to call the Restful API and decipher the strings that you need to have the HTTPClient object call with. Once you know that, then you can set-up the properties in the HTTPClitny object properly. If these calling conventions are not used properly, the Post method will constantly fail.

Regards ... Chris