Problem with Redeem webpage

I have bought a prepaid code for Minecraft from Amazon because the Official Minecraft website wouldn't allow me to buy it. I then went to redeem my code and if I click to redeem it on the main webpage it has a page not found error. When I've managed to get on the redeem page by using a different link, it gives me the error "you need to enter profile name" even though I've already entered a profile name that it says is okay. Ive tried it with multiple profile names that show up as okay but then get the error as soon and I hit "redeem".