Document number

Document number is a unique identifier you assign to each accounting or billing document, such as an invoice, credit note, receipt or purchase order. In the UK it’s the number that lets you track the document and keep a clear audit trail; on invoices it’s commonly shown as the invoice number. For VAT invoices, use a unique, sequential number that clearly identifies the invoice.

You can run separate number series for different document types or business units, but keep each series sequential with no unintended gaps. If you void or cancel a document, keep its number reserved and mark the document as cancelled so the sequence remains traceable.