Sonarr can't connect to any downloaders, but Radarr connects fine

Sonarr Ver. 2.0.0.5344
Docker container
Ubuntu 20.04 LTS

I tried to add qBittorrent as a downloader using the same settings as I did in Radarr (localhost, port 8080, user, password) but it can’t connect. I also tried with Transmission and had the same issue. Does anyone know a fix?

Thanks!