I had set first as well a user with PUID and GUID, run into same issues, after struggling i just removed the different user and run it under root, i know that is not the solution but it works for now.
What i need to do and you as well is to make sure your directories which you use for your download client (transmission/deluge etc) are accessible by the same user as you set in sonarr or its not able to use these.
Then you need to add the paths under the Volume and Bind mounts. If you have not set these then stop the container, click modify and set it, before that be sure your user can access it, you could test this on the command line by going to it while being that user.
Once you have set the paths start the container again and test if you see the paths in sonarr under system / disk space should show up there.