For reasons as yet unknown rclone has been banned from Amazon Drive.
All attempts to get tokens are met with "Client authentication failed: invalid_client". And you'll find rclone has disappeared from your authorized apps in your Amazon account.
This only affects Amazon Drive, it doesn't affect any of the other cloud providers that rclone supports.
Amazon haven't been returning either my calls or emails so I don't know exactly why this has happened or whether it is possible that the ban will be reversed - I will update this post if and when I learn more.
I have now heard back from Amazon. Rclone has been banned for having the encrypted secrets in the source code.
I've asked for new credentials so I can build an auth server and get rclone going again - I haven't heard back on that reply yet, but it is plausible we could get rclone running again with Amazon Drive in the not too distant future.
Thank you all for your patience
I've finally heard back from Amazon about my request for new developer credentials (after 10 days!) to build an auth server
We have ended the Amazon Drive API and SDK invitation period to focus on enabling new customer experiences with current developers. Should this change, we will provide an update on our developer website: https://developer.amazon.com/amazon-drive
So I guess that is a no
See this forum post for a workaround.