Before completing a manual refund, be sure to check the account for a TC 971 AC 665 (indicates a manual assessment has been made). Clearly state the decision regarding the refund.You must apply for a refund or a transfer of credits result- ing from overpayments within six years of the date of the overpayment or credit. If the payments made exceed the amount of tax liability, the amount of the overpayment is shown on the applicable line in the Refund section of the Form 1040. Over Payment Refund Letter To Customers Template. Form TR210 is a letter you receive if: If you received it, you may be entitled to a refund for the tax year stated on the letter. Yes. You just need to call the customer care and tell them you paid it twice. They will immediately refund it to your account. First, you need to issue a check to your customer using the Accounts Receivable account for the overpayment amount. This brief but important letter notifies a customer that he or she has overpaid you.