Amazon really doesn't want anyone doing this, and have made it a PITA to get it to work. They shut down most posts on reddit or XDA when anyone posts a real tutorial about it.

Shame on Amazon.

My "workaround" is to just use my TV's built in Amazon app. It's more difficult to use than an Android TV app would be, but at least I don't have to go downloading things from relatively unknown sources.

there is just do a search for. Though I hear the quality is not that great.

I heard there's a way to sideload the mobile or another systems apk of it, but apparently content is locked down to 720p or it might've even been 480p, don't remember.

Amazon TV Launcher, it works great and the Amazon video app does work pretty well on MiBox. I forgot where I found the apk but whoever made it did a great job

But I'm able to use Amazon video fine on my mi box, a friend of mine bought mi box seeing prime video working on mine,. When he received prime video didn't work in factory box, we Uninstalled Netflix as we don't use , next updated the Ota to latest , then don't know it started working 😀, it was the shield tv apk of amazon prime we tried..