The function outstanding invoices will show any existing invoices of the same invoice holder, so that the new postings can be added to an existing invoice.
You may add to existing invoices until the invoice is included in the outgoing invoice journal (night run). Changes to the invoice after this are not permitted.
Press the button outstanding invoices to search for and select the respective invoice in the invoice overview-dialog. To search only those invoices which have not been settled completely, enter yes under part account, which will facilitate your search.