You can add your Mettle card to Google Pay in the Mettle app.
From your ‘Account’ screen, tap ‘Add to Google Pay’ and select the device on which you’d like to activate your Mettle card.
Alternatively, you can add your Mettle card to Google Pay from the Google Wallet app directly:
On an Android device, iPhone or iPad, open the Google Wallet app and tap ‘+’ to add your Mettle card.
On a computer, sign in to Google Pay and click ‘Add payment method’.