A payment item subtracts the amount of a customer payment from the total amount of an invoice. You need a payment item when you receive a partial payment toward the amount of an invoice at or before the time you create the invoice.
If you receive full payment at the time of the sale, use a sales receipt form instead of an invoice with a payment item.
Tip: If you enter a payment method, you can group the money you receive by payment method when you deposit it (all checks in one deposit, all Visa charges in another deposit, etc.). Simply create a separate payment item for each payment method your customers use.