NTFY via tunnel?

I have installed the docker container for NTFY and it runs fine when I use the IP address of my local machine. I want to be able to receive the notifications when not on local network. I set up a new Cloudflare tunnel, and a new subscribed topic.

However, when I run "curl -d 'NOTIFICATION' <<cloudflare Public hostname>>/topic", the command simply executes with no response (unlike when I use the local IP address instead of the public hostname.

When I try "send test notification" through the app to the tunnel domain name, nothing happens.

Anyone get this working?