https://www.read.gov.sg/join-the-readsg-challenge
It seems like turning points into money is just a happens to exist sort of mechanic. Enough to write a headline that they are technically "paying you". The real mechanics are much more typical gamification. Like earning xp, streaks, leaderboards, limited edition goodies at events, prize draws, collective goals.
The strict money payout is S$0.02 per 15 minutes at most once a day. Obviously if you were doing this it would be more for the rest of the dopamine then hoping to buy a candy bar after like 50 days.