A payment receipt is a written acknowledgement that a good or service has been received and paid for. A payment receipt is different from an invoice because an invoice can be issued on credit, but a payment receipt is verification of payment having been received.
Payment receipts are used to prove ownership of items. They are often necessary if goods need to be returned or exchanged because retailers ask for proof that the item was bought from their company. Also, payment receipts are required for any warranty issues and are necessary for rebates. Payment receipts are important for tax purposes as well.