When a monitor is down you can set up a webhook to send a message to a Discord channel. You can set up a webhook in the Discord settings. The webhook URL should look something like this: https://discordapp.com/api/webhooks/123456789012345678/abcdefghijklmnopqrstuvwxyz1234567890

How to set up your Discord webhook

https://support.discord.com/hc/en-us/articles/228383668