Got an overpayment notice, what now? (Spokane)

I received a letter saying I was overpaid about $600 on my claim. I have read a lot of threads here and could not find my exact situation. The letter mentions an appeal window and a repayment plan. Has anyone disputed one of these?

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.