Field FM commitment string &1 not assigned to US ledger &2

What causes this issue?

The US Federal extension of the Budgetary Ledger (BL) is active. You
need to select the field commitment string &V1& as a split field for
this ledger &V2&.

System Response

It is not possible to calculate the "Delivered" and "Paid" amounts
without this requirement.

How to fix this error?

Select this field commitment string &V1& as a split field for the ledger
indicated (&V2&) using the split processor customizing.

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.