The reason you are seeing a $0 balance could be one of the following reasons:
You have not yet redeemed a rebate coupon. See How to Redeem my rebate coupons ("Redeem Rebates" button).
Your rebate is still processing. You can check the status in your “Account” tab under "My Rebates".
If you had a balance before and you no longer see it, you most likely “cashed out” to your PayPal account. Please check your PayPal account to see a deposit transaction from Flipp.