Permalink to post_series returns 404

Everthing works fine but the permalink https://…/post-series/slug/ does return a 404. Is there any chance this has to do with the plugin? I fiddled around with permalinks and tried a lot of stuff but it is persistent.

Would you know of a certain test scenario I could launch or am I missing something in the work flow? I created a post series, display and navigation works fine, it just does not link to the entire series, or shouldn?t that work out of the box?
Cheers and thank you for any insights!