Cannot connect to Gitlab Registry on self hosted install

Hi,
I enabled the registry in gitlab.rb, planning to use the same domain name with a different port:

# docker container registry
registry['enabled'] = true
registry['registry_http_addr'] = "localhost:5000"
registry_external_url 'https://gitlab.mysite.net:5050'
registry_nginx['ssl_certificate'] = "/etc/gitlab/ssl/cert.crt"
registry_nginx['ssl_certificate_key'] = "/etc/gitlab/ssl/cert.key"

and check permissions on the cert

chmod 600 /etc/gitlab/ssl/*

Then, when I try to connect to the registry, I get a failure:

$ docker login gitlab.mysite.net:5050 -u <user> -p <token>
WARNING! Using --password via the CLI is insecure. Use --password-stdin.
Error response from daemon: Get https://gitlab.mysite.net:5050/v2/: Service Unavailable

I checked in the log file tail -300 /var/log/gitlab/registry/current but see nothing relating to logging in.

I’m on self-managed GitLab Community Edition 13.8.1

I have many runners, all for CI, but do not see any listed for registry, should it? Also, running docker ps on the server when no CI/CD jobs are running is empty.

Do you have any ideas what I can do to get this working?
Thanks!
Christopher