I keep having this issue--I made a mistake applying a payment, if I edit the payment it adds the same amount due twice to the invoice. If I delete it, it sends it back to the original balance due instead of a partial payment, this specific invoice has 5 payments and I had added two payments when one was still pending. If I issue a credit and have to send the statement to the customer, they'll question what it is as it shows there and I don't want it to make it seem like I'm overcharging or doing something I shouldn't.