A sales invoice is a document sent by a seller to a buyer, detailing the goods or services sold and the amount due for payment. It records the sale of goods or services, with all pre-agreed terms such as quantity of goods, price per unit, total cost, and any taxes or other charges that may apply. The purpose of a sales invoice is to provide both parties an itemized record of the product or service purchased and the means of payment. This allows customers to easily track orders placed, while allowing sellers to efficiently manage accounts receivable. By issuing sales invoices, businesses are able to accurately measure customer demand and cash flow.