Is Cashback Boost Card, Cashback Boost Card Sitewide and Friend Power Card stackable?
If you own both Cashback Boost Card and Friend Power Card and they are both available to redeem, you can choose which one to use on your pending purchase and they are not stackable as in the screenshot below:
If Sitewide Cash Back Boost Card is already activated, you will not see apply button on the Pending Purchases list.