Certbot not working with itk-apache
Due to the filesystem-permissions of the "acme"-folder the webroot-validation will always fail if apache is run with the itk-mpm. This is because of the vhost is running with user and group of the web+client of the domain to be checked which has no access to enter or read the "acme"-folder in ispconfig's frontend location. I suggest to move the folder from ispconfig's frontend to e.g. /var/www and change the permissions to 0755. The renew-config-files under /etc/letsencrypt/renewal should be adjusted accordingly.