Having a weird problem with one domain (let's call it: ispdomain.com ) that refuses to generate a Let's Encrypt certificate for its website All the other domains on this server and all work perfectly with the automated Let's Encrypt SSL setting staying ticked and valid certificates issued. I suspect the problem is because when I installed Ubuntu 18.04 & ISPconfig 3.1.15 I named the server VPSserver1.ispdomain.com and system mail name mail2.ispdomain.com. The problem is limited to the website [www.]ispdomain.com even though I have checked the basics: Client limits: SSL available Let's Encrypt available Website config ticked: SSL Let's Encrypt SSL No matter what I try the certificate never gets created and the Let's Encrypt SSL box unticks itself which I think means there was an error while generating the certificate but I have no idea how to diagnose that any further. If I use a manually generated *.ispdomain.com certificate from sslforfree.com by using _acme-challenge DNS TXT records, then https://[www.]ispdomain.com works perfectly but that is not ideal as it will need re-doing every 90 days. Another odd thing is if I attach to the server as http://VPSserver1.ispdomain.com I get the default apache page as expected but if I use https://VPSserver1.ispdomain.com I get the certificate and website content from the very first customers website that was created. Also if any other client does not configure their site correctly the https responses also default to the certificate and website from the first website created on the server. Have I made some fundamental installation error? Can it be fixed without having to rebuild the server from scratch again which would be a nightmare ?