About 500 users have passed the quiz since launch (despite frequent offs due to bugs, running out of money, running out of daily quota, etc) but I observe some share of fraud too. It is not very large but concerning. To reduce the incentive for fraud, the reward will now be reduced to $2.50.
Maybe what you should do is ask users to pay $8 worth of byteball to take the quiz, then if they successfully complete it you'll send them $20 worth of byteball back