Duplicity: UnsupportedBackendScheme: scheme not supported in url: s3+http://foo.woof.com/?
The bug has been fixed by Duplicity developers. A patch against for the problem is now available.
Details: See the bug report
I know this thread is old as but if you still receive this error, run the command with "-v 9" for verbose output. For me it complained that the 'psutil' package was missing on the server, so I installed it with 'pip3 install psutil' and all was fixed.