It’s not actually illegal. He is paying a lottery to people who register to vote. Similarly, Cards Against Humanity is paying people who didn’t vote last election to make a voting plan.
It’s illegal to pay someone to vote regardless of if it’s for a side. Neither instance goes far enough to be considered against the law as written. Cards Against Humanity states that it shouldn’t be and it’s fucked up that it is.
It doesn’t pay you to register to vote. I read the whole website when it started