Hi Chyuche
welcomer to the Apple (user-to-user) Community.
Re: Gift Card: must be redeemed in USA storefront . What do I do
Apple support have an article online (link below) that may be helpful:
If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support
There's a discussion thread on a similar issue:
Redeem gift card from another country - Apple Community
says:
"The best solution would be to give it to somebody who uses the USA store".
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Apple Support's article: Check your Apple Account balance – Apple Support
says:
"You can't redeem or return Apple Gift Cards, App Store & iTunes Gift Cards or unused Apple Account balance for cash, except as required by law."
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If needed:
Apple phone numbers around the world:
Contact Apple for support and service - Apple Support
All the best :-)