In my case it was failing as the IP of my source server was not whitelisted in the target server.
For e.g. I was trying to access https://prodcat.ref.test.co.uk from application running on my source server. On source server find IP by ifconfig
This IP should be whitelisted in the target Server's apache config file. If its not then get it whitelist.
Steps to add a IP for whitelisting (if you control the target server as well) ssh to the apache server sudo su - cd /usr/local/apache/conf/extra (actual directories can be different based on your config)
Find the config file for the target application for e.g. prodcat-443.conf
RewriteCond %{REMOTE_ADDR} <YOUR Server's IP>
for e.g.
RewriteCond %{REMOTE_ADDR} !^192\.68\.2\.98
Hope this helps someone