Ledger &2 assigned to company code &1

What causes this issue?

You have assigned ledger &V2& to company code &V1&.
Postings exist in company code &V1&.
To ensure the consistency of the data for a company code that is already
used, other activities need to be performed, such as the following:
Define assignment time/date
Ensure completeness
Build opening balances of the new ledger
This function can only be performed with the assistance of the SAP
General Ledger Migration Service.

System Response

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

How to fix this error?

If company code &V1& is already used in your production system, you need
to cancel the assignment and start by activating the migration service.
Otherwise, it is not possible to update the posting data consistently to
the ledger or to build balances.
If company code &V1& is not used in your production system, you can save
the assignment in this step. In this case, however, the data in the
ledger will not be complete, and the system cannot create opening
balances for the ledger.
If company code &V1& has been created as new, you can save the
assignment in this step and create the data by transferring it from the
feeder system or by using opening postings.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.