You are not allowed to specify a key word

What causes this issue?

A key word can only be specified for display types 'TXT' and 'TXD'.

System Response

How to fix this error?

Choose a different display type or delete the key word. SAP recommends
that you do not use key words, if possible. Instead, you should always
use display types 'DD1', 'DD2', 'DD3' and 'DD4'.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.