Posting sales and purchase invoices is a key accounting process that allows a company’s commercial transactions to be recorded correctly (Accounting Act, Journal of Laws 1994, No. 121, item 591). Posting sales invoices: A sales invoice is a document confirming the sale of goods or services, containing details of the seller, buyer, subject of the transaction, price, and VAT rate. The posting process: receiving the invoice (paper or electronic); verification (formal and substantive correctness); posting (to the appropriate revenue account, and recording the output VAT); archiving. Purchase invoices are posted on the same principle, to the cost or asset accounts appropriate to the purchase, recording the input VAT.