The output of this command is
grep: /usr/local/hestia/data/users/admin/../../conf/dns-cluster.conf: No such file or directory
Error: dns-cluster host ns1.domain.tld doesn't exist
the issue is caused by the execution of the line
is_object_valid "../../conf/dns-cluster" 'HOST' "$host"
is not changing its path to /usr/local/hestia/conf/dns-cluster.conf