Taxonomy for non-CustomPress post type

Anyone got experience with CustomPress and LearnDash? I want to add custom taxonomies to LearnDash topics. So I created a new taxonomy in CustomPress, and assigned it to sfwd_topics. So now topics has a taxonomy field, cool. Alas, the taxonomy link gives a 404 page. It may be a CustomPress limitation? Or a feature? Maybe I need to also create a custom post type? Or?? Can’t taxonomies stand alone?

Any thoughts?