if you're a wow player, you can pay for the game using the wow token items you buy ingame. costing you no money; think of how you can sell virtual items from cs:go and tf2 for steam wallet money.
incase you didn't know, these tokens can be brought off the auction house and converted to account balance, which can then be spent on blizzard games in the app. (they can also be spent on wow time if thats what u really want i guess)
with the huge demand for them,
prices have skyrocketed in EU