@Dani8504 what type of reader do you have? If you use a Kindle or the Kindle App, you need the mobi version.
For another type of reader you need the mobi.
Once you determine the correct file version you need, download to you computer then send file as an "attachment" to your "reader email" as instructed on 2 Tigers LLC website.
Let me know which one you don't need so I can have company send you refund for that purchase :)