Custom Sounds not working ?

Custom sounds in a resource pack, when not replacing preexisting sounds, do not appear to be working at the moment, when using the playsound command to initiate them.

It may be possible that I'm incorrect on this, but I attempted with my resource pack namespace rather than "minecraft:", without the aforementioned resource pack namespace, and with variations of file paths separated by periods & forward slashes, & no combination seems to be functioning.