Hi @fschmid - welcome to the community! 
While this doesn’t use a webhook node, you can probably take some inspiration from this post from @MutedJam on how to fix up this workflow:
Since you mentioned you had a JSON template, it can show you how to utilise it and then also make a HTTP request. It’s a good starting point!
By the way, if you’re totally new to n8n, it might be worth checking out our Beginner’s course to help understand some n8n concepts.
Let me know if that helps, and if you have any other questions!