Re: I can't find where to redeem my Sims 4 gift card

@Acid_St0rm120  Choose the item you want to buy, and when you're asked for a payment method, click "EA Wallet."  From there, click "Add funds to your EA Wallet," then add the product code for the card.  You might have to scroll down a bit to see the field.

Alternately, go to ea.com, sign in, click your profile picture, and choose Account Settings > Payment Methods.  From there, you can click the button to add funds to your EA Wallet and enter the card's code.