"This code can only be used in [country]" means your gift card's region doesn't match your Google Play account's region.
Three Ways to Fix It
Option 1 (recommended): Buy the right card
- Check your account region: Google Play → avatar → Payments & subscriptions
- Buy a card for that exact country at marix.app
- Redeem — no more error
Option 2: Change your account region to match the card Google Play → Settings → Country and profiles → change to the card's country (once per year limit).
Option 3: Use the card in a matching account Create a new Google account set to the card's country, then redeem there.
How to Avoid This in the Future
At marix.app, each gift card clearly shows its region (Turkey, USA, India, etc.) in the product name. Always verify before buying.
Summary
Region mismatch error — fix by buying the correct regional card at marix.app.