However, kept getting an error that failed to validate notification url when I tried to subscribe. The notification url I used is the http post url generated when http request is received action in the handler workflow. The notification url includes everything after invoke? Then I tried https://******.sharepoint.com/your/webhook/service, it still doesn't work.
Could anyone have used Power Automate with webhook advise what is wrong with using the http post url as the notification URL? If not used, handler workflow won't be triggered to detect what has been changed and run approval workflow.