Ntfy is good. Are you using the F-Droid or Google version of Amethyst?
Is everything up to date?
If I recall correctly, notifications didn't work for me the first time I set it up either. Not sure, but I believe it started working after a software update from either Graphene, Amethyst, or ntfy. I may have troubleshooted it, but I can't remember.
But why wait, why not just tackle them all and be done with it, right? Not sure what troubleshooting you've done thusfar, but
**Is ntfy working for you otherwise?**
If not, then try removing the connection to Amethyst, clear the ntfy app cache and storage and reboot the phone.
It might not be necessary to do a full phone reboot, but I would.
**If ntfy isn't otherwise working after you test it.**
Take a pic of any settings, keys etc you need to backup and completely uninstall it along with Amethyst, then reboot the phone and try connecting again.
That should do the trick, or hopefully lead you further towards identifying the issue. Lmk how it goes.