Bonus Bets

Online betting is now in my state. All the commercials are yelling about “bet $5, get $300 in bonus bets.” I know that the bonus bets cannot be withdrawn, and if I win with them, I only get the profit not the money I bet with. All that is fine.

But what is to stop me and a buddy from just using our bonus bets against each other to ensure one of us wins?

Team A is playing Team B. I bet Team A, he bets Team B. One of us has to win. Profit.

What am I missing?