SAP Message TU278 - You cannot delete budget billing plan &1 (deregulation)

Diagnosis
The budget billing plan (&V1&) you want to delete belongs to aninvoicing service provider. In the budget billing plan, a budget billingrequest was created for at least one item and has already beenregistered to the invoicing service provider.

System Response
INCLUDE ISU_VERARB OBJECT DOKU ID TX

Procedure
Reverse all budget billing requests
Delete the budget billing plan