Please accept my sincere apologies for the silence on this. I have now completed a fix for the Amazon integration and it will be released as a beta soon (currently in review by Google).
Unfortunately, the amount of support requests I get would be a full time job already, so I strictly prioritize spending time on actual development of the app. I do read and consider most emails though.
That said, issues with the Amazon integration are always hard to fix, as I need to reproduce them on my own Amazon account (which also means that I have to actually purchase stuff regularly just to have an active order to test on)