Simple enough. Do you have any way to prevent fake scores? Not sure it would even be possible for someone to cheat, but still. Something like having a random float at the start of the game that multiplies the actual score and that you verify before sending the score online, so someone can't just change the value of their score in game.
Also, I didn't mention that in my first comment, but when playing on my phone, I couldn't type in a name for the Leaderboard, feels like you might have lost a couple of potential players because of that.