I have used playsound,
and did the command
/playsound entity.enderdragon.death @p ~ ~ ~ 1 1 1

And it said: That player cannot be found

So then i tried my name, TheYukonBear.

/playsound entity.enderdragon.death TheYukonBear ~ ~ ~ 1 1 1

It still didn't work. I tried it with another sound, and still doesn't work.
I am in a superflat world, on a multiplayer server without mods or plugins and is opped.