Amazon is discontinuing access to their Cloud Drive API, meaning that Duplicati will not be able to read or write files from Cloud Drive after August 16th 2019.
If you are using Amazon Cloud Drive, you should start moving your files away from Cloud Drive while there are still tools that can access the files. After August 16th you will need to use the Amazon Drive tool to retrieve your files.
Duplicati itself will be updated soon to warn users that rely on Amazon Cloud Drive.
The full message from Amazon is here:
On August 16, 2019, Duplicati’s integration to the Amazon Drive API will be discontinued. Customers of Amazon storage will continue to have access to their content through our first party applications for Amazon Photos and Amazon Drive. Please make arrangements to discontinue all traffic to the Amazon API before August 16, 2019.