Overpayment letter from the unemployment office - 2 weeks in

The agency says I reported earnings incorrectly, but I think I followed the instructions. I have read a lot of threads here and could not find my exact situation. I did not notice any errors at the time. Who should I talk to first?

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.

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