create a sub domain with external tld and dns

How can I do add a sub domain website where the name server is provided by the base domain hosted on a different server.
I was able to add it but noticed the Let’s Encrypt certs generation failed and acme requires extra efforts.
Greetings from the beautiful Moselle!

 

Just add the website in ISPConfig with the full name "sub.example.tld" and then create the DNS record pointing to the IP of your webserver accordingly.