Process and Apply a Payable to a Receivable at the Same Time
You mean that you want to post a vendor invoicc against a customer invoice and do that in one transaction using a manual journal?
I belive that should be possible,. But you can no do it directly from the purchase invoice or sales invoice functions in Business Central.
You might however have to use the blank document type. Because you can not have a different document type in the same transaction.