Got an overpayment notice, what now?, bookkeeper here

After 2 weeks of benefits I got a notice saying I must repay some of it. I worked as a bookkeeper before this. I did not notice any errors at the time. Who should I talk to first?

Keep everything in writing and save the confirmation numbers. It saved me later.

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.