Import Failed Error in Sonarr

Sonarr version (exact version): 2.0.0.5322
Mono version (if Sonarr is not running on Windows): 5.20.1.19
OS: Ubuntu 19.04
Debug logs: https://pastebin.com/LZyxme8N
Description of issue: Sonarr is not importing downloaded files. Not sure if this is a permissions issue, or just me messing up the setup of Sonarr.

Additional Information:
I have my OS installed in an SSD, and the download path is set to a 2TB HDD I have.

I am running Transmission Torrent Client/VPN in a docker container from here.

Any help would be appreciated. I have spent so much time on this I’m out of ideas as to what to do, every step brings up a new problem lol.

19-7-1 19:44:56.7|Error|DownloadedEpisodesImportService|Import failed, path does not exist or is not accessible by Sonarr: /data/completed/sonarr/Euphoria.US.S01E03.1080p.AMZN.WEBRip.DDP5.1.x264-KiNGS[rarbg]

On the sonarr side, can you browse to /data/completed/sonarr/? Imo the easiest is to do a manual import in sonarr and (try to) browse to the path.
If you can see part of the path in sonarr, but can’t get to the underlying folder(s), it’s likely a permissions issue.
If you can’t browse to this exact path in sonarr, but you can find the downloads somewhere else (e.g. /dev/sda1/...): you’ll probably have to set up a remote path mapping in sonarr, so it knows to replace /data/completed/sonarr with the path it can actually see.