FBL1N displays supplier line items. Open items remain unsettled at the selected key date; cleared items have a settlement recorded by that date. The report amount shows the supplier exposure represented by the selected documents. A payment block is an additional control, so an invoice can be open and due while still excluded from a payment proposal.
Choose the supplier and status scope before adding totals. A report showing all suppliers can answer a different question from a report for one supplier, even if the same document appears in both. These tasks use the original opening invoices and prepared payment histories. Read the status at the requested date. Don't treat every invoice on the report as ready for payment.