This sounds like the better display of returned errors (beyond status code) that I’ve long been wanting. Although you’re after Google Drive errors (and 403 has annoyed me too), is it a general HTTP helper?
It’s done using a GitHub pull request but I don’t do them so can mostly refer you to public information.
How to join in the development of Duplicati?
Proposing changes to your work with pull requests (GitHub’s documentation, but other info is around)
Maybe someone who is more familiar with this will stop by to help, but that’s the basics of how it goes.
After the pull request gets put into the master branch by somebody, the next step is a Canary release.
These tend to happen when enough changes build up or an emergency happens (like fixing Dropbox).
Ideally they would happen more often, but there is a need for someone to volunteer to do the releases.
Duplicati seeks volunteers in all areas such as forum, manual, test, and most importantly development.
Regardless, thanks for the code!
EDIT:
Actually, my 403 errors were on uploads, so possibly that’s a different problem. Regardless, any extra information that can be displayed would be helpful (and hopefully not be too long or have private info).