"Present balance" is the total amount of funds you have in your wallet. This balance includes any pending cash back that has not been issued. If the cash back is in a pending state it cannot be withdrawn, until the transaction has been cleared. Once the transaction has cleared, the pending cash back will no longer be in a pending state. It will now reflect in your "available to withdraw," so you'll be able to withdraw those funds.
In your wallet, "available to withdraw" includes the amount that you are able to transfer to your bank or PayPal account. This does not include any pending cash back that has not been issued. You must have at least $25 in your "available to withdraw" balance to be able to withdraw any funds. If your present balance is higher than your available to withdraw, then you must wait for your pending cash back to be issued. This pending cash back has to be cleared by your credit card processor first.