
You're absolutely right — the Omit Default Descr. in Jnl. setting does not apply to the Bal. Account No. field.
From my observations, when the Account No. field is not empty, Business Central correctly takes the Description value provided in the API request.
However, when the Account No. field is blank, the system ignores the provided description and instead uses the Bal. Account Name as the description.
Here’s the relevant section of the standard logic in the Gen. Journal Line table:
[EventSubscriber(ObjectType::Table, Database::"Gen. Journal Line", 'OnBeforeIsAdHocBalAccDescription', '', false, false)]
local procedure OnBeforeIsAdHocBalAccDescription(GenJournalLine: Record "Gen. Journal Line"; xGenJournalLine: Record "Gen. Journal Line"; var Result: Boolean; var IsHandled: Boolean)
begin
if GenJournalLine.Identifier then begin
Result := true;
IsHandled := true;
end;
end;