WBS element & must be an account assignment element

What causes this issue?

The activity or activities that you want to assign to a WBS element, are
in a network with an account assignment. The WBS element must also be
an account assignment element in order for you to assign it (them),
You cannot make any actual or open item postings to the WBS element &V1&
because it is not defined as an account assignment element.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Enter a WBS element that is defined as an account assignment element.
If you really want to post to WBS element &V1& then you must first have
it changed to an account assignment element by an authorized person
(for example, the system administrator).
Procedure for the system administrator:
Define the WBS element &V1& as an account assignment element.

Error message extract from SAP system. Copyright SAP SE.