This brief but important letter notifies a customer that he or she has overpaid you. It can serve as a very good customer relations letter.The salary overpayment resulted because . We have identified the following overpayment and are in good faith voluntarily refunding all monies collected in error. Create a professional overpayment email template with our AI assistant. Type a letter to the person who made the payment, explaining that he paid in excess of the amount due.