ususally it makes no sense to expose an application using different internal and external fqdn. As bluepuma77 stated already some applications might redirect to a "default" URL other might reject access on a "wrong" domain.
Other issues arise as well - if your "internal" domain is not accessible from the internet yu can not issue public TLS certificates for this domain. I'm under impression traefik will request TLS certs for all exposed FQDNs so the request may fail completely. I would recommend to access publicly available server using public FQDN only and use "split brain DNS/split horizon DNS" for internal access. and only use "internal"entrypoint for application not exposed to the public.
