SvelteKit: Slug Route within a Group Route

I have this SvelteKit directory setup: routes/(main)/vergabeassistent.Within that directory I have:

• +page.svelte
• [slug]/+page.svelte

Calling localhost:5173/vergabeassistent works fine and is a list view. I now wanted to create slug route for the detail view and the id is a parameter in the url. However, calling localhost:5173/vergabeassistent/SOMEID is not being found at all. I suspect this may be caused by the fact that I am already withhin a the group route of (main)?The +page.svelte of the slug route looks like this:

<script lang="ts">    import type { PageData } from './$types';    export let data: PageData;</script><h1>{data}</h1>

What am I doing wrong?