Purchasing documents already exist for a condition record

What causes this issue?

Purchasing documents already exist for a condition record. When a
purchase order is created, the system logs all transactions/events that
are relevant to "subsequent settlement" accounting and updates the
appropriate database table.

System Response

The function you requested (e.g. deletion of the rebate arrangement) is
no longer possible due to the existence of relevant purchasing
documents.

Error message extract from SAP system. Copyright SAP SE.