Seller issue an invoice to a purchaser
Sellers issue an invoice to a purchaser whenever goods are sold. It indicates the number of products purchased, the price for each product and the total price for the transaction. When an invoice is received, it means the seller is demanding payment according to agreed upon payment terms.
The usual payment for an invoice is in cash, but sellers may allow credit transactions for regular buyers where the customer is allowed to pay for the good at a maximum number of days. Sometimes the seller offers special discounts when the payment is done early.