It seems the amazon kindle has changed something in the new published kindle books. It requires the latest kindle app to download it.
Now we are working on this issue. Once there is a solution, we will let you know. The older kindle books still can be cracked with Epubor Software.
There is still another way to remove drm from this kind of kindle books if you have any kindle eink device registered with your amazon account. Please download the kindle books via "Download and transfer via usb" and then remove kindle drm with Epubor Ultimate. Here is the detailed guide: https://www.epubor.com/how-to-remove-drm-from-kindle-kfx-ebooks.html#meth4
