Every day, a new card can be claimed for free in the in-game Shop. To claim it, click the Shop button on the left side of the home screen. Note that when you have an unclaimed free card in the Shop, a small indicator with an exclamation mark will appear on the Shop button.
Navigate to the free card by scrolling to the “Daily Deals” section.
Press the “FREE” button to claim your card. A confirmation dialogue will pop up to inform you of your new card!
Note that if you already own a full set of the daily free card on offer, claiming the free card will count as a surplus (duplicate) card, counting as progress in your weekly crate.