Thirty seconds here saves the most common problem on this site. A gift card that will not redeem is almost always a region mismatch, and it is the one failure we cannot reverse after the fact.
What a region lock is
Gift cards are issued by a brand's operation in a particular country or market, and they only redeem against an account registered in that market. The restriction is the issuer's, built into how the code is generated. Nothing we or you can do changes it afterwards.
It exists because brands price differently by country, operate as separate legal entities per market, and settle in local currency. A US Amazon code is a claim against Amazon.com's US entity, and Amazon.de simply has no way to honour it.
The ones that catch people
Amazon. Every national Amazon is a separate store. A US code works only on amazon.com. We list Amazon US and Amazon.de separately for exactly this reason, and we will add others on request.
Steam. This is the subtle one. A Steam wallet code is tied to the store region your account is set to, not the country you are sitting in. If you moved countries and your Steam account still says its old region, buy for the region the account says. Steam also refuses to add a balance in a currency that does not match the account's.
PlayStation, Xbox and Nintendo. All three are strictly region-locked to the account's country, and all three make changing a console account's country difficult or impossible once there is a balance on it.
Apple. Locked to the App Store country of the Apple Account redeeming it. Changing that country requires spending your existing balance down to zero first, which is a genuine obstacle.
Netflix, Spotify, Disney+ and similar. Locked to the country the subscription is billed in.
The ones that are not locked
A few genuinely work anywhere: Roblox, Discord Nitro and Booking.com are the ones we carry that are global. We mark them "Global" rather than with a country code.
How to get it right
Check the account, not yourself. Open the brand's site, look at the account's country or store setting, and buy for that. Where you physically are is irrelevant — a German living in Spain with a German Amazon account needs the German code.
For a gift, ask the recipient what their account region is. Guessing from where they live is how this goes wrong.
Where we state it
On the brand tile, on the product page, on the checkout page and in the order email. Four times, because this is the thing worth repeating.
If you get it wrong
Tell us straight away with the order code. If the code has not been redeemed we will sometimes be able to exchange it for the right region, depending on the brand and how long it has been. If it has been redeemed, or the brand will not take it back, it is spent and there is nothing we can do — which is an unsatisfying answer and the honest one.
What we will not do is pretend we can fix it and then go quiet. If it cannot be fixed you will be told immediately.