I just bought a gift card n it says it been used already
How does this happen?
Question marked as
See -> If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card
If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support
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Card has already been redeemed
If you see a message that says that your card has already been redeemed, you might have already redeemed it. Sign out of the App Store or iTunes Store on all of your devices, then sign back in. This refreshes your Apple Account balance. Learn how to check your Apple Account balance.
If you need more help, contact Apple Support.
Beware of -> About Gift Card Scams -> About Gift Card Scams - Official Apple Support