You cannot delete all sub-items for item &

What causes this issue?

You cannot delete all sub items of item &V1&.
Possible reasons are that the item
is used as a reference (there is a subsequent document)
was created using complete reference
is used as basic item for an alternative item
cannot be deleted because of make-to-order production (there is a cost
collector for the item)

Error message extract from SAP system. Copyright SAP SE.