Service Procurement: Purchase order item &1 &2 is not consistent.

What causes this issue?

Service Procurement is only allowed for valuated goods receipts with
account assignments, together with goods-receipt-based invoice
verification.
The Work Item ID and the Service Performer must be supplied (they must
exist in the reference document).

System Response

The GR/IR (goods receipt / invoice receipt) account maintenance cannot
be processed for purchase order item &V1& &V2&.

How to fix this error?

Contact your system administrator.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.