Item is part of a payment order and cannot be changed.

What causes this issue?

When items which are part of a payment order are cleared, no changes
can be made (e.g. with a cash discount amount, cash discount percentage
rate, setting items as inactive). An item must be cleared exactly as it
stands in the payment order.

System Response

The system informs you if you try to make any changes to items.

Error message extract from SAP system. Copyright SAP SE.