Substrings are not allowed in transparent matchcodes

What causes this issue?

A field of a matchcode ID was defined as a field component by
specifying the offset and length. Field components, however, are not
permitted for transparent matchcodes (update type = 'I').

System Response

In this case it is not possible to activate the matchcode ID.

How to fix this error?

Cancel the field component definition by cancelling the definitions in
the columns "offset" or "length" (e.g. with the reset character
'!') in the matchcode ID field maintenance screen. The system then
automatically uses the length of the base table field on which it is
based.

Error message extract from SAP system. Copyright SAP SE.