Hello Ahmed,
Just trying to avoid prototyping the system this time... As I understood no issue to G/L P&L "cost" without a cost element, but an issue with G/L P&L "revenue" without a cost element?
Please check field status groups for that G/L account, maybe WBS is mandatory there.
If the issue is really around the second G/L account master data you can test that by specifying the first G/L account as receiver.
Thanks,
Paulo