General Ledger Accounting Customizing must be adjusted (see long text)

What causes this issue?

The system has already found existing ledgers. Either standard scenarios
or customer fields are assigned to these ledgers. Customizing for New
General Ledger Accounting must therefore be adjusted.
Note:
Technically, when Funds Management is activated, the application
indicator, which amongst other things is used to identify the general
ledger, is set from GLF to PSM.

System Response

It is not necessary to activate Funds Management.

How to fix this error?

Perform the following activities: These do not happen automatically so
that you can decide whether existing ledgers should still be used in
Funds Management.
You have two options:
You want to keep the existing ledgers. Run report
FMGL_CHANGE_APPL_IN_LEDGER (compare SAP notes 834815, 840783 and
906397). This report assigns the existing ledgers to Funds Management.
You want to create new ledgers after activating FM. To do this, perform
the following steps:
Delete the assignment between <DS>
<DS:SIMG.VC_FAGL_LEDGER_DC>Scenarios and Ledgers</></>.
Delete All Assignments<DS>
<DS:SIMG.VC_FAGL_LEDGER_DC>Customer Fields to Ledgers</></>.
Activate Funds Management.
Create a new ledger and assign it to these <DS>
<DS:SIMG.VC_FAGL_LEDGER_DC>Scenarios and Customer Fields</></>.

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

Technical Background
Once you have activated Public Sector Management, you may no longer see
existing ledgers of the application (GLF) even though they still exist
in the Customizing tables. Settings in the ledger for Customizing are
used to generate coding (such as field transfers). The steps mentioned
here are necessary so that coding is not created for ledgers that are
not used.

Error message extract from SAP system. Copyright SAP SE.