What is the ID of the 'MessageReceived' sound on macOS?

Question

I'm trying to use the 'ReceivedMessage' sound on macOS using AudioServicesPlaySystemSound() but I can't seem to find the ID anywhere. What I've tried:

1. I've looked under /System/Library/Components/CoreAudio.component/Contents/SharedSupport/SystemSounds and couldn't find it either - although MessageSent is there.
2. I've tried AudioServicesPlaySystemSound(1003) as well following this link but that just results in silence. Any help would be greatly appreciated!
3. I've tried looking in Messages > Show Package Contents which only led to more disappointment.
4. I found the file here but I was a hoping to just link to it directly rather than including the .caf file in my app bundle.