OK, does it work from the ssh command line terminal? So if you type in curl http://192.168.1.4/hotwateron.php does it work, HA will need the full path to curl probably /usr/bin/curl and you will probably need to setup the permissions for homeassistant to use it.
Can you trigger it from the frontend in HA via the automation, find it in the frontend and click on it’s name, then in the card that pops up click trigger, does that work?
I can successfully execute /usr/bin/curl http://192.168.1.4/hotwateron.php in ssh command line terminal.
In the frontend, I TRIGGER, it says “service/automation called.”
Now probably the trouble is the permission for HA to use curl. I’m still looking for the way to grant the permission
However, I really thank you for your patience