Came across this in Westpac rewards. Looks like dessert is sorted.
Spend $30 or more in a single transaction on your Westpac Credit Card by either the primary or secondary cardholder. Limited to 1 cashback transaction(s). Cashback is limited to 1 card per customer, per retailer and will be paid into your account within approximately 7 days. Offer is valid for online purchases only. Offer cannot be used in conjunction with any other offer. Cashback won't be applied if you switch the card used to pay after the order has been placed.
IMHO, CBA is better as they give the Yello offers to Debit Card holders too