This is a reply to an old post, but references something I was struggling with and this was the best search result I found ... regrettably it was not answered with a real solution.
Here is what I ended up with that works to start playing a specific Spotify playlist:
Using an App start block, set the following:
Package = com.spotify.music (selected from drop-down of installed apps)
Action = View
Data URI = spotify:playlist:{playlistid}:play
You can get the playlistid by examining the link generated by sharing a playlist. The link generated will be in the form:
Copy/paste the letters/numbers between the last / and the ?.
I hope this is clear enough that it helps others who are attempting to do the same.
-Stuart