Your letter must include your name, address, Social Security number, and why you disagree with the determination. You must complete and return the Application for Overpayment Waiver (DE 1446UI) to be considered for a waiver.The key is to ensure you have a voluntary agreement in writing with the employee before any deductions are taken. In the letter, provide the date that the Notice of Overpayment was sent to you. UC has notified a number of workers that they will need to return what UC claims are overpayments in relation to last year's strike. Follow up with a formal letter that documents your communication and process for handling the error. Step 1: Define the error.