Unplanned service & may not be entered

What causes this issue?

You cannot enter the performed service because there is no value limit
for unplanned services in the associated purchase order.

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 wish to enter this service, the purchase order must first be
changed. Either the service must be included in the purchase order, or
a value limit for unplanned services must be set in the purchase order.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.