The most important part of uploading to Amazon KDP with ebook files is getting the metadata right. This turns out to be a little more complicated than one might expect. Fortunately, others have done the legwork and put the information out there for KDP users.

The following two free titles are well worth consulting on this front:

Let's Get Digital by David Gaughran

Ricardo Fayet's How to Market an ebook

and David Gaughran posted some verypractical tips recently:

https://davidgaughran.com/amazon-book-category-kindle-categories/

and he put up a video too on a related topic before that:
https://www.youtube.com/watch?v=5fXU8R0cHOM

Joanna Penn goes into this topic too in some detail:
https://www.thecreativepenn.com/book-categories-keywords/

https://www.ingramspark.com/blog/the-basics-of-book-metadata-and-keywords