Characteristic &1 does not have category 'CHAR' (character string)

What causes this issue?

You selected a characteristic whose values are numeric (figures with
which calculations are to be made). This type of characteristic is not
supported in this context.

System Response

INCLUDE ISR_VERARBEITUNG OBJECT DOKU ID TX

How to fix this error?

Select a characteristic whose values are of the type "CHAR" (character
string). You can enter numbers as values for this type of
characteristic (e.g. sizes such as 6, 8, 10), if you do not want to
carry out any calculations with these figures.

Error message extract from SAP system. Copyright SAP SE.