/-/metrics returns 404 with Prometheus Metrics enabled

I’ve got a Gitlab Omnibus instance, running gitlab/gitlab-ee:13.5.2-ee.0. On the Free plan.

I have Enable Prometheus Metrics checked in https://gitlab.example.com/admin/application_settings/metrics_and_profiling. However, whenever I visit https://gitlab.example.com/-/metrics, I get a 404, while I would expect to see some dashboards:

I’ve not used metrics before so either I have a misunderstanding about how it works or my setup isn’t working.