Not sure what you mean by payoff. In a normal exchange, you see the price and it goes up and down. In betting, you see the probability going up and down. It's

Not sure what you mean by payoff. In a normal exchange, you see the price and it goes up and down. In betting, you see the probability going up and down. It's also the multiplier on what you will win. In the previous example, they would bet £5 at 50/50.