In the last two days I have been trying to install a new server with Debian 10 and ISPConfig. It is a replacement of my old Debian 7 server that experienced harddisk failure. I followed the instructions in the article "The Perfect Server". The installation went fine. I set up DNS and added a site with SSL certificate. When I test the server locally e.g. https://192.168.1.40/ I get an error "This site can’t provide a secure connection". It doesn't matter what browser I use, the error persists. With Debian 7 I did not have this problem. I suspect that with Debian 10 IPv6 has preference or 'primary focus' while in ISPConfig I set up everything with IPv4, just as with Debian 7. I do not feel like hacking around in the apache scripts as it might mess up ISPConfig. What could be the problem?