I do not have any categories configured at the moment, but I had before (not sure if that is important).
can anyone tell me why I can not save a listing if I do not have a (non-existing) category configured?
meaning, there is no category option on the listing page anymore, but I can not save a listing without it.
I believe all listings must be assigned to a category in order for HivePress to function as intended. However, you may be able to bypass the validation error by editing the listing in the backend of WordPress, but this may break other things like you’re experiencing now.