Not sure what to even look up in KB to undo/solve the problem.

A customer has a balance due on an invoice on their statement that should have been completely paid.

I applied check payment to a customer invoice but it only applied the $1.50 discount and left a balance of $73.50. The full $73.50 was received and deposited with the batch. Do you do a credit memo or is there another way to show the payment has been made in full?