Why is Shadowsocks giving me an "ss-server permission denied" error?

The issue you're running into has to do with file permissions. Shadowsocks does not have permission to access one or more files/directories necessary to start the service, so you'll need to go through the error log and fix the file permissions. You can check the error log for Ssmanager by using the command systemctl status ssmanager.service. Depending on what output you receive, you'll want to ensure that Shadowsocks has the correct configuration permissions for the files mentioned in its /etc/systemd/system/shadowsocks.service, along with the correct file pathways for starting and stopping the service. This Github post describes a similar error and may be helpful as well.