Greetings,

When buying in-game currency, the Google Play Store scans your device’s Google accounts, automatically charging the top-most account with a registered payment method. In other words, if your top-most account doesn't have a registered payment method, but your second account does, it will automatically charge your second account. If both your first and second accounts have payment methods, Play Store will always try charging your first (top-most) account.

To ask the Play Store to charge a different account, please follow these steps: 

• Go to Settings and then tap Accounts.

• Move the account you want to use to the top of the list by removing all accounts above it. To do this, tap on the account(s) you wish to remove, then tap the Menu button in the top right corner and select 'Remove'.