Assigning PM Order to WBS Element & is not Allowed

What causes this issue?

You want to assign one or more <DS:GLOS.maintenance_order>maintenance
orders</> to <DS:GLOS.WBS_element>WBS element</> '&V1&'.

System Response

The current status of WBS element '&V1&' does not allow the assignment
of maintenance orders.
INCLUDE KEINE-FUNKTION OBJECT DOKU ID TX LANGUAGE E

How to fix this error?

To carry out this assignment, you must change the status of the WBS
element '&V1&' in such a way that the assignment of PM orders to this
WBS element is allowed.

Error message extract from SAP system. Copyright SAP SE.