Order price unit cannot now be changed

What causes this issue?

You already posted a goods receipt and/or an invoice as well for the
purchase order item (compare the purchase order history). As soon as
such documents exist, you can no longer change the purchase order price
unit in the purchase order item.

System Response

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

How to fix this error?

If you still want to change the purchase order price unit, you must
first cancel the goods receipt document or the invoice.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.