No editing of maintenance items for service processing purchasing

What causes this issue?

You wanted to create, change or display a
<DS:GLOS.maintenance_item>maintenance item</>.
You cannot process maintenance items separately for service processing
of purchasing.

System Response

For service processing of purchasing, a
<DS:GLOS.maintenance_plan>maintenance plan</> always consists of
exactly one maintenance item and is bound tightly to this. Therefore,
special processing of maintenance items is not planned.

How to fix this error?

You have the following options:

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

In create mode, choose another maintenance plan category.
In the change or display mode, choose another maintenance item, whose
maintenance plan category allows the maintenance item to be processed.

Error message extract from SAP system. Copyright SAP SE.