If you can‘t redeem your App Store & iTunes Gift Card, Apple Music Gift Card, or content code - https://support.apple.com/HT201195#differentcountry --> Card or code is from a different country or region:
"App Store & iTunes Gift Cards and Apple Music Gift Cards are specific to your country or region. If you're trying to redeem an App Store & iTunes Gift Card or Apple Music Gift Card that was purchased in a different country or region, make sure that you're redeeming it in the iTunes Store for the same country or region. You can't redeem cards outside of the country or region of purchase. For example, an App Store & iTunes Gift Card purchased in France can't be redeemed in an iTunes Store in the U.S."