Got an overpayment notice, what now?, barista here

I received a letter saying I was overpaid about $400 on my claim. 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?

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

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.