Overpayment letter from the unemployment office - any advice?

The agency says I reported earnings incorrectly, but I think I followed the instructions. Thank you in advance. The letter mentions an appeal window and a repayment plan. Who should I talk to first?

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

Read the letter for the appeal deadline and act on it, even if you think you will end up repaying. Then ask about a payment plan.