Paying for a gift card online for a friend in the US

[confusedteacup]

I have a good friend in the US and for her birthday I really wanted to buy her a 6 month membership for spotify online through their website. Spotify isn't available in my country at the moment (I live in the Cayman Islands but used to use the service when I lived in the US) but I can still get to the part of the site to buy subscription gift cards. However I don't have a valid zip code since I guess you need to live in the US just to buy a gift card. 

I don't understand why i wouldn't be able to purchase the gift card for someone else that will be able to use the service. If anyone knows how this could be fixed please help I really want to surprise her for her birthday at the end of the month!! Obviously I can't buy physical cards if those exist because the service isn't available here.