Many of the 'things' in OrbitKit are related. A Venue has Blueprints. An Exhibit is associated with a Blueprint and a Design. An Archetype contains Blueprints.
To be safe, OrbitKit prevents you from deleting things that are still associated with other things. You cannot delete a Blueprint until you have deleted all the Exhibits associated with that Blueprint (or reassigned them to another Blueprint).
If you try to delete something that is still being used by another 'thing' in the system, you get the "Unable to delete {Thing} because it is still in use" error message:
The solution is to unwind this from the bottom up.
Unable to delete an Archetype? Remove all the blueprints from it. Be careful, this will destroy any associated exhibits too!
Unable to delete a Blueprint? Destroy any associated exhibits, or move them to a different blueprint. If you are using archetypes, remove this blueprint from all archetypes (adding another blueprint from the same venue will allow you to 'recycle' existing exhibits for most platforms).
There are two exceptions to this:
You can delete a Venue. This will delete all the Blueprints and Exhibits automatically. The delete is immediate; listings will not be taken down from the marketplaces. Be careful, this cannot be undone!
You can delete Designs. This will cascade the delete to related Exhibits, but will pull listings down from the underlying platform. If you do not want this behavior, first freeze the exhibits. Frozen exhibits will be deleted without touching the marketplaces.