Differences between a payment receipt and a sales receipt
A payment receipt is a proof of payment. It is mostly for the buyer rather than for the business. It is typically not used in accounting for digital products. A payment receipt lets a buyer be sure that their payment was received by the business.
By contrast, a sales receipt (a.k.a simplified invoice) is a bill or (request for payment if that payment has not already happened). Sales receipts must contain a more detailed breakdown of the costs and taxes involved, as well as information about the business. They also must have a unique receipt number and a few other strict requirements. Unlike an invoice, it does not require customer information, making for less form field to fill out at checkout for your customers (as long as the transaction falls beneath the threshold required by your tax authority).