You need a US address.
The problem is that e-books re treated differently then DTB. For some silly reason it is legal for Amazon US to sell and DTB to anyone in the world but they cannot do this for ebooks. Harry explained it once and I went "That makes no sense" and promptly forgot his very excellent explanation.
Many e-books are georestricted, not sold to people outside of specific countries. Every country has had a problem with this. There are books that Americans cannot buy from Amazon.UK. Most of the complaints about book availability come from countries without an Amazon specific e-book store, so every place but the UK and the US.
It is very frustrating for folks. The work around is to use a US address (not something silly like the White House or Amazon headquarters), gift cards (no way to check the credit card billing location), and some folks use a site to mask their ISP addresses although there are folks who have had success without this bit.
This is going to be the case for anyone who wants to buy a book outside of the US or UK regardless of the type of device. Geo restrictions effect all retailers. It is not the fault of the retailed it has to do with different publisher holding the rights in different countries and legal agreements.