There can be only one clustered index

What causes this issue?

You have set CLUSTERED YES for a secondary index and you set the index
memory parameters for a table that does not (yet) exist in the database
or that does exist in the database but that does not have a primary
index or a clustered primary index.

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

As you did not set CLUSTERED NO for the primary index, a database error
would occur for the non-existent table if it was created in the
database or for the existent table during a conversion.

System Response

How to fix this error?

If you really want to create a clustered secondary index, you must set
the primary index to CLUSTERED NO.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.