Amazon brought out the new Kindle Previewer 3 in February this year and it’s now no longer supporting Kindle Previewer 2.94 and older versions.
If you want to preview your Kindle ebooks before publishing you will need to download version 3 which supports Enhanced Typesetting and gives you a very accurate representation of what your ebook will look like when delivered to Kindle devices and apps.
You can also continue to preview your ebooks on the previewer located in your Kindle Direct Publishing account.
Kindle Previewer 3 offers a bird’s eye view of your book and you can check over the overall layout. When Enhanced Typesetting is enabled for your book, you can preview pages as adjustable thumbnails, allowing you to validate your book faster than before.
Amazon is no longer providing software and security updates for Kindle Previewer 2.94.