iTunes Users, please look here:
http://www.spacetimestudios.com/showthread.php?7704-Cannot-Purchase-Platinum
Android Users:
Some mobile browsers do not work correctly when attempting to purchase Platinum. If this is the case for you we recommend trying from a PC.
https://auth.pocketlegends.com/WebStore/store.jsp
Enter your Pocket Legends email address and password when starting, then your Google Checkout or Amazon username/password when purchasing.