A webhook, an http request to a server initiated by an outside service, is difficult to test. The outside service must have a valid url to make the request with, but your development server generally runs on the unreachable
The Ngrok product page describes ngrok like this:
It connects to the ngrok cloud service which accepts traffic on a public address and relays that traffic through to the ngrok process running on your machine and then on to the local address you specified.
If I have a local dev server on port 3000 I run
ngrok like so:
> ngrok http 3000 Forwarding http://92832de0.ngrok.io -> localhost:80
Then, configure the outside service to point the webhook at the
ngrok.io address provided by the ngrok tool. Now, your local server will receive http requests from the outside service and you can evaluate those requests effectively.