Hi Nai,
Webhook.site is meant for quickly testing what an event trigger will send you in the payload, including anything in the headers, like auth tokens. This site can be helpful when developing a client service so you can see the data and where it is in the payload so you know how to access it. It can’t be used to develop an actual client service that you can use in a production environment.
I realize that the current documentation on event triggers doesn’t walk you through how to actually build a client service that subscribes to a trigger, which is why I’m working on improving the entire event trigger developer experience this quarter, including an example app, blog post, and video tutorial. One thing I’m considering using for the tutorial is ngrok, which is a tunneling service that exposes your localhost to the internet so you can test your event trigger client locally before deploying to a production environment. You might consider using ngrok for development purposes in lieu of webhook.site.