Excerpt from documentation for setting up GitLab Pages with wildcard DNS entry: https://docs.gitlab.com/ee/administration/pages/#wildcard-domains
external_url "http://gitlab.example.com" # external_url here is only for reference
pages_external_url "http://pages.example.com" # not a subdomain of external_url
pages_external_url
should not be a subdomain of external_url. But why is that, since there are no problems doing it that way.