If people aren't paying their debts, garnish their wages, seize their assets, or if they're flagrantly avoiding paying back debts, put them back in jail--you know, normal things that we already do which actually get people to pay back their debts. Failure to pay reparations is a legitimate concern, but it's not relevant to voting rights.
Let's not pretend this is about reparations. It's about disfranchising people.