For anyone still looking to use Spotify within LMS controlled via Vera and start a playlist, I've managed to do it this evening. I am using the 3rd party Spotify plugin in LMS.
You need to add your Spotify playlist to your LMS favorites as I couldn't get a playlist to start but favorites do.
Click on the name of the Favorite and you should then see the URL for the playlist, copy this into the LUA code below replacing the BOLD text and obviously replace IP address with your LMS server IP and MAC address to the address of the client you wish to control.
I've used the following LUA in a scene:
local client = socket.connect('192.168.0.110', 9090)
client:send("b8:26:eb:c1:71:f0 playlist play spotify:user:takethatofficial:playlist:7o1E5PXj3e0KNOUgRaU56A\n")
I hope this helps someone else :-)