Quote from a recent message on the Amazon Kindle forum (someone had the same sync problem):
"ok... found this mentioned in another thread -
take a look at the Nook App you download - what version ?
OK I figured out why I was having problems. I was downloading the Nook for Android app from getjar.com and found out this is an older version of the Nook app.
I found a later version (18.104.22.168) at:
After downloading the app and logging in, I was able to see all my previously purchased books."
I'm curious. The Kindle Fire cannot just install apps from the Google Play Store, only their own walled garden of apps? Sounds like the older Nook Tablet. So how does this GetJar work?
The Kindle Fire has never been restricted to just apps available from Amazon's store. It's true that you can't install apps directly from the Google Play store, but you've always been able to configure it to install apps from 3rd party sources like GetJar. So the Kindle Fires have never been as closed off as the B&N-developed Nook tablets have been.
I don't own a Fire tablet, but I've gotten them for my folks and had to help them set it up. If I remember correctly, there is a spot in settings that you can activate to allow apps to download from "unknown sources".
Here is some information from Amazon's help pages that might relate to what you are discussing.
Thanks!! This worked perfectly.