The Payout modifier multiplies the amount from the value parameter by the percentage you set. In other words, this is a ROI calculator.
ROI = ((revenue - costs) / costs) * 100%
Your conversion value is $5 and you're willing to pay 40% of it for ads. 40% of 5 is 2.
ROI = ((5 - 2) / 2) * 100%) = 150%
Thus, your ROI will be 150%
⚠️ The conversion value taken from the postback. Therefore, you need to properly set up your conversion tracking.