Coin purchases can take anywhere from 1-5 minutes for the coins to transfer over to your balance. However, if you still do not see your coins, it is recommended to relaunch the application after what you will probably see the pop-up.
To relaunch an app:
Press the Home button two times quickly (or swipe up from the bottom of the screen and pause while still pressing the screen). You'll see small previews of your recently used apps.
Swipe left to find the app you want to close.
Swipe up on the app's preview to close it.
If the coins have still not been transferred over, please reach out to the support team and make sure to include as many details of your purchase as possible (date and time, amount, coins/package purchased, etc).