Typically an invoice is used when you supply items to a buyer & they pay at a certain timeframe like 30 days. An order is a buyer ordering supplies that you don't stock, they pay a deposit & at time of delivery or ready to ship they pay the balance. Receipts are for paid in full before shipping.
If these are all online sales you would want to be paid in full prior to shipping. Invoicing & orders are ideal if you are an actual store with accounts that buy on credit.
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