I read a sci fi book where ads were effectively a micropayment mechanism. You built up credit by watching ads, and you couldn't do certain things online when yo

I read a sci fi book where ads were effectively a micropayment mechanism. You built up credit by watching ads, and you couldn't do certain things online when your ad credit was too low. So you could have a screen with lots of ads open in your loungeroom for an evening and top it up.