I had never heard of this game and had to do a google search for it.
Apparently it's an F2P game (free to play), but one player said this:
However, unless you want to wait literally YEARS to get anywhere in the game, you have to buy the in-game currency, called diamonds, for real money.
There are those people who are willing to be patient and wait for some time so that they can progress in such games without spending real money (and it is doable), but some players might find this a turnoff to enjoying the game.
Maybe someone else here has firsthand experience with it. I also do not know if this would be considered to be a "casual" game.