Extension def does exist and has correct perms:

rust@rust:~/RustDedicated_Data/Managed$ ls -l | grep Discord
-rw-r--r-- 1 rust rust 381440 May 2 13:21 Oxide.Ext.Discord.dll

And I did fully restart the Rust server after installing. I'm using LinuxGSM to manage the server if that might make any difference.