Add variable to http get

I’m setting up my Google home so that it can send commands to kodi through http get. I’d love to be able to say “start film {1}” and then it play. To do this I figured I could send the rpc command:

http://my-ip:8080/jsonrpc?request={“jsonrpc”:”2.0″,”id”:”1″,”method”:”Player.Open”,”params”:{“item”:{“file”:”special://profile/playlists/video/SpokenMovie.xsp”}}}

And then have a smartplaylist where “title contains {1}”

However I am struggling to find where, or if, I can sent this variable within the command. Something similar has been done in voxcommando here:
https://youtu.be/0b3V2BwuE-s however that is on a local network within a software, not using the app directly