Sadly the only way that i am awear of is you must buy credits. I found the easiest way was to sms wat they ask for and enter the code. once this is done i dont think you will be restricted anymore throughout the game.
hope this helps
Urban Rivals | Free Online Manga Trading Card Game | TCG | MMO
The Urban Rivals team is made by lovers of all kind of Collectibles Cards Games and Trading Cards Games like: Magic the Gathering, Dominion, Vampire, Yu-Gi-Oh!, Pokemon, Wakfu TCG, Assassin Creed Recollection, Shadow Era, Kard Kombat and Might & Magic Duel of Champions.