Finally able got it working. Turns out it was a firewall issue and needed port 443 open.
From the nabox appliance, best way to check is using the following command:
nc -vz -w 5 ip-address port-no
The response should come back as
FQDN ip_address 443 (https) open
I think anything other than that, then further investigation is required. As in my case it was port not allowed in the firewall