As of 27 Aug 2020, Valve made some changes to Steam Wallet Codes redemption recently to reduce gift/game card scam. These changes should not impact regular customers who enjoy using Steam wallet codes they purchase in their local currency. You have to buy country specific codes according to your Steam account’s country.
Each Steam User Account is associated with a specific currency, which you can see in the top right corner of your Steam Client.
Going forward, you may encounter an error if you try to activate a Steam Wallet Code issued in a different currency than the one of your Steam User Account.
If you have questions about your ability to redeem Steam Wallet Codes, please contact Steam Support.
If you have a Steam account, you can report gift card scams online here.
Keep the Steam card itself and your receipt for the Steam card. Learn about Steam gift card scams and how to report them here.