403 errors after setting up SSL

I have a VPS, hosting plan and domain name all with OVH. It's been running fine for 3 years. I confess I never really understood exactly how the SSL gateway worked, but it seemed to!

After having enabled SSL within the hosting plan today for my domain and the www subdomain, and obtained a certificates, I now get 403 errors (Forbidden You don't have permission to access this resource.) on both http and https.

The OVH error log for the website says: AH00032: Symbolic link not allowed or link target not accessible

The site is accessible and working fine on both its IP address and server name, so I'm assuming the problem is something to do with DNS linking the domain name to the site, rather than a problem with firewalls, ports or something else on the site itself. Does that sound right?

Everything looks right in the DNS zone. I have type A pointing to the IPv4 address for my hosting plan, and type AAAA pointing to the IPv6 address.

Only clue is this on the SSL Gateway page: IPv4 DNS State showing 'KO' - which I assume is bad.

!26|690x91

Any suggestions to what might be wrong?

EDIT: I realised that in the DNS Zone, IPv4 should possibly be pointing to the address for the SSL gateway, so I've changed that. Also allowed the four outgoing IP addresses from the SSL gateway in the OVH firewall for my server's IP address. I am now getting Error 503: Backend unavailable.