Number & not in external interval

What causes this issue?

You entered a number which is not in an external number interval.

System Response

INCLUDE 'KEINE-VERARBEITUNG' OBJECT DOKU ID TX LANGUAGE E

How to fix this error?

Enter a number which is in an external number interval.
If you do not know the range of the external number interval, use the
pushbutton "Information" in the window "Create PM Order: External
Number".

Error message extract from SAP system. Copyright SAP SE.