VPN SSL issue

We have a VPN setup which works when we use the IP Address of the WAN however it shows the VPN Certificate warning saying "The certificate you are viewing does not match the name of the site you are trying to view" which obviously we do not want showing. If you click view cert its the correct cert and click ok you can connect.

I have read that I should be using my subdomain which is the same as the internal network domain so this error isnt there. But  when I try connecting the Forticlient just says "Unable to establish VPN connection"

What I have done:

- Setup SSL VPN following Fortinet guide

- Installed SSL Certificate on Fortigate 60E for our domain (network.example.com)

- Pointed the A record for our subdomain (network.example.com) to the WANs IP so you can ping it fine 

Any ideas where I am going wrong?