It might simply be that Play Store’s servers are overloaded, depending on their workload and the time of day. In consequence, in-game purchases can be greyed out until the servers are back to normal. This issue is usually fixed after a short period of time.
For additional help, tap on the detail icon, which provides you with information regarding what might have gone wrong. You may also need to:
- check your login/connection with a valid Google account
- check your Google Wallet account at wallet.google.com and make sure that your payment method and billing address are correct
- simply wait a little while and try again, servers may have been busy
- update your Play Store app
If these don't help, double-check that you have a valid payment method linked to your Google account. If you have added additional Google accounts to your device, keep in mind that the Play Store will always attempt to charge the account with a registered payment method at the top of the list (which can be found on the account list in your device's settings).
You might also want to get in touch with your credit card company and/or bank if you use a credit card as your primary payment method as they often place holds on in-app purchases.
If you are still having trouble making purchases, we recommend heading over tohttps://support.google.com/googleplay/digital-content/?hl=en for further help with respect to Google Play and the purchasing process on Android devices in general.