So curl is trying to reach ntfy via http? Have you tried redirecting http traffic to https and also adding an endpoint for it?
- "traefik.http.middlewares.ntfy-https-redirect.redirectscheme.scheme=https"
- "traefik.http.routers.ntfy.middlewares=ntfy-https-redirect"
Also, i'm not sure which version of traefik you are using, but traefik.port is no longer used. Try:
- traefik.http.services.ntfy.loadbalancer.server.port=80