There is one game I like to play which is a completely free game. There is a new feature called lottery where I am guessing you pay with game points for a chance to win something. Is that considered a sin in that case? It is impossible for a person to pay money for the game points. They are only earned in the game. Not sure if it's still a sin, even though no real money is lost. What is lost in this case are virtual assets.
What is being gambled are things that have no value, though it did cost you time and game playing to accumulate the points being gambled. However, there is a problem with influence. The game is teaching the players that gambling is acceptable and for some that will spill over to real life.