No it can’t be void, it should be a function.
If you use sendsync() your code should work, but I think you supply wrong data, the “user” field should be the user key. You find that in the dashboard when logged in at pushover.net.
@ejeklint: to prevent confusing more users, I suggest you correct your post from March 1, where you use sendasync() with no params.
Fair enough. 
Any update on a general release of the latest software?
We’re just fixing up a few bugs that some early testers have found… soon!