For Android phone and tablet

The first payment method you add to your Google Wallet™ app will be the default way to pay for all in-store purchases. To change your default payment method so that it is your Westpac Mastercard®

1. Open the Google Wallet app
2. At the top, swipe from the right edge of the screen until you find the card that you want to use as your default
3. Tap the card
4. At the bottom, tap Details > Make default for tap to pay.

For more details, go to Set or change your default payment method - Google Wallet Help

For online payments, you can select which card to use each time you make a payment.