Question
Why can't I delete a Pipeline/Stage/Activity Set that is not in use?
Answer
Have you checked the deleted items in your recycle bin?
If a record is deleted and sent to the Recycle Bin, it may still have a Pipeline/Stage/Activity Set attached. The Pipeline/Stage/Activity Set cannot be removed from Insightly until it is no longer associated with any records.
You will need to either restore the record and remove the Pipeline/Stage/Activity Set or delete the record completely from Recycle Bin.