Hi, I got a gift card for 100 euro bought in Europe, but I can not put it on my U.S. account. What should I do? Thanks

Send it back to Europe to someone who can use it.

Gift cards are country specific.

Sorry

iTunes gift cards are only valid on accounts based in the country in which the card was issued - so if you have a US account then you can only use US gift cards. Do you know anybody in the country where you bought it from that you could sell or give it to ? Or you could try selling it on a site such as eBay.