Sometimes (not in this instance) the error message is completely worthless. I remember one time trying to configure automatic backups in Cloud Native Postgres and it just wasn’t working, the errors were opaque. So I asked on the project’s github what the problem was and the devs were quite unhelpful. Some random user came along and said “Oh you need to set the S3 region like this…” and backups started working.

Jdownloader 2 is the most straightforward.