Cost element & & is not found (check entry)

What causes this issue?

The key that you have maintained for the cost element does not exist.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Check whether you have entered the key correctly. If necessary, change
your entry.
INCLUDE 'NA_ALLG_VORGEHEN' OBJECT DOKU ID TX
Check whether the key is defined for the cost center. Define it if
necessary.

Error message extract from SAP system. Copyright SAP SE.