Error 400 when trying to download a file

Dropbox doesn't offer a way to retrieve request/error logs like that, but I'll pass this along as a feature request. I can't promise if or when that might be implemented though.

A 400 error like that would indicate an issue with how the request was formatted, and in cases like that we recommend using client-side logging to inspect the requests that the client is making. You may want to refer to the documentation for the network client you're using and see if you can enable some client-side logging and use that to inspect the request when you reproduce the error.