Not sure if this helps, but I'm also running #0xchat set to ntfy. I think this is working?? Whenever someone sends a DM, I get that weird 0xchat default squeak, but strangely, no notification visible in the pull down notification view. So I'm not sure what to make of that. Perhaps this is expected behavior for 0xchat, and ntfy is working with it properly. 

 Can you see the notifications when you open the ntfy page in the browser?  

 Just checked both 0xchat and Amethyst URLs using their ntfy links - nothing. Just says "You haven't received any notifications for this topic yet."