Just a follow-up. I've added the attrs.xml file to the res/values folder. One thing with my project, is that I am trying to integrate the ads in into a library project. The way my apps are setup, I have most of the code in a library project and I'm not sure if it's causing this issue. I've tried everything and I can't get it to find the 'adSize' attribute.
I figured out the issue. If you're using a library project you have to use "lib" not "res" in the namespace, eg:
http://schemas.android.com/apk/lib/com.my.app Thanks for the heads-up Amazon. Now I'm getting a new error: java.lang.IllegalArgumentException: Invalid ad size string. See documentation for available ad sizes even though I'm specifying a string of "320x50", which seems to be a valid size. Hey Amazon, could you have made it any harder to implement your ads?