You purchase game credits with Tokens, which you can buy in the Store tab. There are free ways to get Tokens like watching videos, answering surveys, and completing offers, but if you want instant Tokens to get to playing faster, purchasing Token packs is a great way to go!
At the top left of your Play Screen, you’ll see your game credit count (the number of bingo cards, golf balls, diamonds, etc. you have left). Tapping on that or on the "Get [game credit]" button in the bottom left of the Play screen will take you to the Store page. From here, if you tap on the Tokens tab on the right you’ll be able to buy packs of Tokens. If you already have Tokens, you can head straight for the game credits tab on the left to use them to buy more game credits for the S2Rewards game you're playing!
Once you’ve paid for your Tokens, you can pick them up from your Inbox along with any game credits once you buy them.