Told I owe money back on my benefits - 13 weeks in

After 13 weeks of benefits I got a notice saying I must repay some of it. 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?

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.