Firts of all thank you for the game and making everything in the store 0 credits. I was always wondering what some of these things do. But when I try to buy something I get this notification. I'm horible at computers did I do something wrong? btw I'm not doing anything in the game just standing.

If you go to your inventory, then select the gold text in the drop down menu (it'll have the name of the island you're on at the top) you can change your costume :)