Service &: quantity & exceeds quantity & in purchase order

What causes this issue?

In the case of planned services, the work must be done exactly as
defined inn the purchase order,,
(service specifications/quantity).

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

System Response

How to fix this error?

If you wish to record the performance of unplanned services, you must
change the purchase order accordingly.
Either include the desired work as a planned service in the purchase
order or set a value limit for unplanned services in the PO.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.