Console Command 'ModifySoundClass' is Unrecognized

When running a game in the editor and using the Command Console 'ModifySoundClass', the console returns saying the command is unrecognized.

It is my understanding, that even if you do not create new sound classes, all the sounds are placed under the default 'Master' sound class.

I tried using "ModifySoundClass Master = .2" and received the same error message the user is reporting. Perhaps I am using the console command wrong?

I did manage to find a workaround for this issue if users are attempting to set the overall volume within their games.

Workaround
https://answers.unrealengine.com/questions/32217/best-way-to-adjust-global-audio.html

1. Create a new First Person BP Project with Starter Content
2. Add the 'StarterMusic' Sound Cue to the Level.
3. Create a new 'Sound Class' and call it something like 'MusicSoundClass'
4. Assign the newly created 'Sound Class' to the 'StarterMusic' Cue
5. Open the newly created 'Sound Class' and check 'Is Music'
5. Press Play (PIE)
6. Bring up the Console Command window and type "ModifySoundClass MusicSoundClass Vol = .02"
7. Notice there is no change in volume while playing, as well as the error message within the console command window saying the command is unrecognized.