When I manually create a web hook through my development store's [Settings / Notifications / Webhook] screen, my HMAC calculation matches. For this scenario, I am using the key displayed at the bottom of the screen.
However, when I create a web hook through the REST API, the same exact code for HMAC calculation fails. Here are the steps I take:
1) Delete all manually created web hooks
2) Create a web hook using REST
3) Use the "API Secret Key" in my application "App Setup" screen in place of the key provided by manually created web hooks.
I am receiving the hook in my web server which means the web hook has been successfully created. Seems like the "API Secret Key" that I am using is wrong.