Tokens are premium currency and therefore can be exchanged into “normal” game currency.
But you cannot change “normal” currency into premium currency because that would void the exclusiveness of premium currency and hence its value and meaning.
“Free” online games mostly have this setup into normal currency and premium currency.
The premium currency can be used to buy better things in general, change to normal currency, buy additional attempts / fuel / energy (whatever the game uses to limit the amount of actions of the player) but in exchange you can only get a little of it for free in the game and have to purchase more with real money if you want it.
Edit: Another often seen important difference between normal currency and premium currency is that normal currency only works in the game you gained it.
But premium currency often is placed above the games which means you can use it for all games of the company as long as you play those games with the same player account.