We email payment receipts. However when customers payments are split, partial, or they have a credit when the invoice is issued, the receipt shows all the items on the bill, the total of the bill, and the amount paid on that occasion. It does not take into consideration past payments or credits, so I spend time fielding calls from confused customers whose receipts appear too be telling them they still owe money or have an outstanding balance.
For example Jane Doe gets an invoice for $200. She pays $150 on Tuesday and has a balance of $50 that has to be paid by Sunday. On Saturday she pays the remaining $50, and her receipt says: Total bill $200, amount paid $50.
On Monday morning she calls me, concerned that she still owes $150. This is particularly an issue with charitable organizations and municipal/county authorities! They often pay the same bill twice, or spend hours querying it.