Buy credits in shop then you can sell on market or go to my colection pick the card yoi want to sell and select sell to kate then you got a offer from kate you can accept then is the card sold
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