Amazon changed something and I can't easily buy Kindle books on my Amazon app any more. Also the buy button is gone from the browser window on my computer!
They said I should be able to do it that way...
Well, maybe that is just a temporary bug?
I checked and it is possible to download a sample and buy it via Kindle App after scrolling to the bottom of it.
"To remain in compliance with Google’s updated Play Store policies, readers will no longer be able to buy or rent Kindle books or subscribe to Kindle Unlimited through this app. You can always add to your library by buying or renting books through amazon.co.uk in a web browser."