Got an overpayment notice, what now? - 5 months and counting

After 3 weeks of benefits I got a notice saying I must repay some of it. I did not notice any errors at the time. Who should I talk to first?

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

I asked for a waiver and a plan in the same call, and they gave me both forms. It was less scary than I expected.