Installed the Oculus integration from the Unity package manager.
Installed the Oculus integration from Asset Store.
Updated the Spatializer plugin from the Oculus menu.
Selected the Oculus Spatializer Plugin in Project Settings > Audio.
Restarted Unity.
Added the ONSPPropagationGeometry script and it worked.
Other issues to note:
ONSPPropagationGeometry throws errors on GameObject's that have a name longer than 30 characters.
If you get an error be sure to reset ONSPPropagationGeometry script before retrying (after shortening file path).
When you bake the ONSPPropagationGeometry it adds a ONSPPropagationMaterial script autmatically, unfortunately it does this every time you bake, so edit / fix this in the script.