All the answers I’ve found in official documentation and on Stack Overflow for finding web hooks are incorrect. The admin area > hooks page does NOT contain web hooks. It contains system hooks, which fire when you create/delete projects and users and things like that. This is not what you want.
To find your web hooks, go to the specific project > settings > web hooks (on sidebar in GitLab 6.1.0) page. These will fire on post-receive for the project in question. You can use a service like RequestBin to see what the payload looks like and to ensure you’re firing these off correctly for debugging purposes.