Tutorial: https://devcenter.heroku.com/articles/app-webhooks-tutorial
So after running this command:
heroku webhooks:add --include api:release -l sync --url https://totel-webhooks-notificaiton.herokuapp.com/webhooks -s 0bf64c0b00d5b7fc624b66032e01be8d3fb4f30bbdfd2eb90ec8c3461ebddde7 -a $TRIGGER_APP
I get belwo image, so that means webhook is added to my target app now: