Data can be only created in the Accrl Engine by transferring legacy data

What causes this issue?

A setting has been made in the Accrual Engine determining that data can
only be created here by means of legacy data transfer (table
TACEDS_LEGACYM).

System Response

The action is terminated.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.