Here's the response I got, for the record:
At this time, the Amazon Drive ended the invitation period with third party apps. I'm very sorry for any disappointment or inconvenience this may cause. This is definitely not what we want our customers to experience.
You can use one of our Amazon Drive apps (available for PC/Mac/iOS/Android) to sync / upload / connect to Amazon Drive. You can use open source code to connect to Amazon Drive another way.
However, I understand that having the feature re-enabled would be convenient and also improve our customer experience if we are able to negotiate and convince the developer team.
Considering your comments as a feedback, I've forwarded your email to our Amazon Drive Specialist Team. They will carefully review your comments and I know they'll want to hear about your experience.
We're regularly working on making improvements to your Amazon Drive experience and will definitely consider your feedback. The Business Team will carefully review your comments.
Thank you for your cooperation and understanding. We look forward to seeing you again.
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