Read a couple of posts here which said to add a WAN rule.
So added a WAN rule with :
Source: My office external IP
Destination (the external WAN ip of the WAN port)
port: 8443 (the port the web gui is on.
Did not work.
As we normally hit the web GUI through a local ip (e.g. 10.10.10.10), via a VPN, I added a NAT rule to map external wan port on 8443 to the 10.10.10.10 on 8443
This did not work either.