It is an electronic-wallet that reflects your Bonus Credits and charges incurred based on your usage within your Zipster Account.
If the value reflected is in green, you are using pre-payment.
If the value reflected is in red, you are using post-payment. These outstanding charges will cleared using the registered credit/ debit card.
Click on "Pay" tab on the function bar located at the bottom of your screen to view your Zipster E-Wallet.