Overpayment letter from the unemployment office - what worked for you?

The agency says I reported earnings incorrectly, but I think I followed the instructions. This is my first time dealing with any of this. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

If you are unsure, free legal aid in your area may help for this kind of notice.

Collect your pay stubs and certification records for the weeks they name. Mine showed the error was a date mix-up.