You are downloading the Music Prime XAP file v220.127.116.11 for Windows Phone. Music Prime is a free and useful Music app: Unoffical Amazon Music streaming app, not affiliated with Amazon. You can now play any Prime music, in your library or not. Also supports Prime ... You can now download the offline XAP file to install & try it.
Download Locations for Music Prime 18.104.22.168 XAP file
Note: To install it manually from an SD card, you should choose one of the server location above to get the offline Music Prime XAP file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.