Error 400 - bad_request

Are you running Duplicati on a Mac?

If so, then even though it’s not exactly the same error, you may find moving to a canary version newer than 2.0.2.8 OR setting the FH_DISABLE_APPLECC=1 environment variable before starting Duplicati might help (all as described here):

Oh, and I edited your post by putting “~~~” before and after the error message to make it easier to read.