I am currently running OS 4.5.5.3 on my Kindle fire HDX. I was able to
successfully download the Android app apk 5.6.0.14 from here
https://www.apkmirror.com/apk/ebay-mobile/ebay/ebay-5-6-0-14-release/ebay-buy-sell-save-money-5-6-0-14-android-apk-dow...
