Very simple script that read all monitors of UptimeRobot and send a notification to ntfy.sh when a monitor goes down.

Copy the config.example.php to config.inc.php and put your UptimeRobot API KEY (read-only key) and your ntfy.sh topic (authentication not yet supported).

php run.php

Try the script and if it works you can run in cron every 5 minutes:

*/5 * * * *	www-data    cd /path/to/script && php run.php