Real-time integr. CO-FI: Ledger group &1 does not contain leading ldgr &2

What causes this issue?

In the customizing of the real-time integration of CO-FI the ledger
group &V1& is used.

System Response

The ledger group &V1& doesn't contain leading ledger &V2&.
This means that the leading ledger can't act as ledger for CO data for
all company codes.
Background:
In SAP S/4HANA Finance FI and CO share the same persistence for storing
postings: In other words, CO has to store its data in a G/L ledger. This
G/L ledger must be the leading ledger.
The customizing migration program evaluates the customizing of the
real-time integration of CO-FI in order to check whether the leading
ledger contains all CO postings: That is, primary postings from FI and
secondary postings from CO (such as repostings and allocations between
cost centers).
<ZH>After the migration, the secondary postings from CO will also be
posted into the leading ledger</>.

How to fix this error?

Keep in mind that these additional postings into the leading ledger will
affect the data displayed in financial reports.

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.