Folder is not writable by user sc-nzbdrone

Sonarr version (exact version): 2.0.0.5301
Mono version (if Sonarr is not running on Windows):5.18.0.240
OS: DSM 6.2.2-24922 Update 3
Debug logs:https://pastebin.com/XjXwLV1s

Description of issue:

Sonarr can’t write on my Synology DS213J NAS even though sc-download and sc-nzbdrone has full rw permissions in DSM settings.

Sonarr version (exact version): 2.0.0.5338
Mono version (if Sonarr is not running on Windows): 5.18.0.240
OS: DSM 6.2.2-24922 Update 3
Debug logs: Not sure how to do this. Sorry.
Description of issue:

I had issues with Sonarr when updating, so uninstalled and then reinstalled. Now I am trying to import existing series on my Diskstation.

Unfortunately each time I try I add the existing file I get the following message: Folder is not writable by user sc-nzbdrone

I have updated the permissions via the steps at https://github.com/SynoCommunity/spksrc/wiki/Permission-Management

Can anyone point me in the right direction? I had problems with Plex last month and had similar issues. I got around this by playing with Terminal. Unfortunately I have limited knowledge on how to do this.