Lootboxes.

Players have a random chance of getting crate while playing the game. Each crate is a pool of item cosmetics with various levels of rarity. To acquire one of them the player must purchase a one-use key with real money. Expending the key on a crate initiates a die roll that determines which cosmetic is unlocked.

That’s the gambling they’re responsible for. What gambling players may of afterward is not the same conversation.