The "Lucky Lottery/Billionaire Spin" package is an additional package you can purchase that is only available right after purchasing an offer. You will have one opportunity to purchase the Lucky Lottery offer after a purchase, but once you exit that pop-up, you won't get that chance again!
The spin is calculated by multiplying the number of coins from your first purchase times the number on the multiplier that you got on the spin/ball.
For example, if you purchased 50,000 coins, and then purchased the "Billionaire Spin" and received the 2.5 multiplier, then the "Billionaire Spin" calculation is your original purchase (50,000) times 2.5, meaning you will receive 125,000 coins total for both purchases.