[noahspaghetti]

Whenever I attempt to add custom sounds into my server, I get this error.

[Sound] S_StartSound(): Failed to load sound '*quake\standard\killingspree.mp3'. File is missing from disk or is invalid.

I'm unsure as to what I should do, whenever I join the server I was able to download the files. The commands work in-game as well, I just can't hear the sounds.

[Enzyoo]

Perhaps Windows is blocking the files?

Try unblocking them by accessing properties.

Or you can open up PowerShell as Admin and a command, for example: dir C:\csgoserver -Recurse | Unblock-File
which will unblock all files in that directory.