Got an overpayment notice, what now? (Seattle)

The agency says I reported earnings incorrectly, but I think I followed the instructions. There are 4 people counting on me, so I am trying to be careful. I cannot afford to repay it all at once. Has anyone disputed one of these?

Thanks for writing this out. I went through something close to it 6 months ago, and it settled down once I kept a simple log of every call and form.