here is the link it says
“The Kindle app is available for most major smartphones, tablets and computers. That means with our free Kindle reading apps, you can buy a Kindle book once and read it on any device with the Kindle app installed*. You can also read that same Kindle book on a Kindle device if you own one.
*For iPhone and iPod, and iPad users:
Purchase Kindle eBooks at Amazon.co.uk from any web browser and when you click to purchase, choose to have the eBooks sent wirelessly to your Kindle for iPad app.”