Thank you for using Apple Support Communities. It's my understanding you're unable to use your gift card since it was purchased for the wrong region. I'm happy to help.
Please review the information below:
If you can't redeem your App Store & iTunes Gift Card, Apple Music Gift Card, or content codeCard 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.
When redeeming Apple Music Gift Cards, make sure to redeem the cards in the iTunes Store for the same country or region. You can't change your country or region while you have an active membership.
Learn more about App Store Top-Up cards in China.
If you need more help, contact Apple.
Have a great day!