Unable to expose port 5433


I wanted to expose port 5433 which is supposed to be the read-only replicas so that I can do some stuff with metabase so I added this:

  internal_port = 5433
  protocol = "tcp"

    handlers = []
    port = 10001

However then doing psql postgres://______@myapp.fly.dev:10001 doesn’t seem to work:

psql: error: connection to server at "____", port 10001 failed: server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.