Looking at the HTTP/SSL Debug information we could see the SSL handshake was failing right after the ClientHello. The Workstation was using TLSv1.2.
The ServerHello was not happening - it could not find an acceptable set of algorithms and we got a handshake failure alert - https://tools.ietf.org/html/rfc5246#section-220.127.116.11
javax.net.ssl.SSLHandshakeException: Received fatal alert: handshake_failure
The https.protocols property was set to TLSv1.2,TLSv1.1,TLSv1,SSLv3,SSLv2Hello.
The options SSLv3 and SSLv2Hello were removed from the properties file and the Workstation restarted.
After this modification we were able to get a successful response from the endpoint.