Thanks for your reply, ts678.
The test connection is successful. No files (or folders) show up on S3, but Duplicati successfully creates a new bucket with the designated bucket name. And yes, brand new setup.
I’m currently trying to upload a folder with about 6000 photographs. When I set the remote volume size to the default of 50mb, Duplicati encounters the error after it has processed about 70 files (which may equate to about 50mb?). If I set the volume size to 20mb, Duplicati encounters the error earlier (after say 25 files), and when I set it to 200mb, it encounters the error much later (after several hundred files). I get the impression that Duplicati is failing to write the newly created volume to /tmp/? I’ve tried changing the directory, but the job still failed. No files are ever transferred to S3 - the whole thing fails before that point.
I’ve read through several other threads on this forum but honestly I’m quite new when it comes to Linux so am perhaps slightly out of my depth.