To make in-game purchases, you need to connect your account via the Game Center settings.

Also, check that you have a reliable Internet connection.

Check your balance and connected payment methods in the App Store settings.

For more information about payment methods and making purchases in the App Store, see these links:

https://support.apple.com/en-us/HT204530

https://support.apple.com/en-us/HT202631 

If these tips didn't help, please get in touch with our technical support team, and we'll be sure to help you.