Hey @twentyoverten, thanks for the detailed post.
I belive the issue is the uuid including /
which messes up the url and causes a 404.
To fix this, double url encode the uuid:
As for the webhook throwing a 500, can you expand the request by clicking the arrow on the right (App Marketplace)? I want to see if there is an error message.
Let me know if this helps!
Thanks,
Tommy