Sign in to the account that owns the balance and review your cart. If G2U Wallet is offered in checkout and the available balance covers the quoted total, select it and continue.
Checkout shows the USD balance and the order's quoted cost. If your balance is insufficient, the Wallet option is disabled and the page shows the shortfall. Top up only if that option is available for your account, or choose another available payment method.
A changed price or balance can require you to refresh checkout before trying again. After payment, open the order for delivery updates and Wallet for the transaction. Do not assume Store Credit and G2U Points are interchangeable.