Only numerical or alphanumerical characters may be used in each section

What causes this issue?

When coding one section you have entered both numerical and alpha-
numerical characters. This is not allowed.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

For each section in the coding, enter either numerical <ZH>or</>
alpha-numerical characters.

Error message extract from SAP system. Copyright SAP SE.