The phrase "Why did you redeem it?" comes from a viral video by Twitch streamer Kitboga, who tricked an Indian scammer during a gift card scam. In the video, Kitboga redeems (uses or cashes in) a fake Google Play gift card code which the scammer was trying to exploit, causing the scammer to angrily shout "Why did you redeem it!" This caught on as a popular catchphrase associated with online gift card scams, where redeeming means to cash or exchange a code or voucher for value, often thwarting the scammer's plans.
More generally, the word "redeem" means to buy back, make amends for, or free from harm or captivity. In everyday contexts, it can mean to exchange a coupon, voucher, or gift card for goods or money, or to fulfill a promise. In the viral scam video, redeeming the code means converting the scammer's fake gift card to prevent him from gaining money.
Thus, "Why did you redeem it?" is asked by the scammer in frustration when their attempt to scam by using gift cards is foiled because the code was redeemed by the streamer instead.
