Without the slash at the end of `my-amazing-post`, this should just create a page without any extension at the exact path:

```text
/post/123456789/my-amazing-post
```

Such that when you go to `example.com/post/123456789/my-amazing-post`, it redirects to the new post URL. We don't automagically do anything to the URL unless there's that slash at the end, in which case we make the `index.html` file (because you indicated you wanted a folder instead of a file).