You have to create the variable (money in our example) in Earwigo before you can use it. Use the Variable tab in Earwigo to create your variable.
Note that if a variable is called “money” in the Earwigo editor screen, it will be called “var_money” in the Lua code. That's to prevent people who don't know much about Lua accidentally picking a variable name like “if” or “end” and causing all kinds of mayhem with the compiler.
The prefix “var_”, which is prepended to each variable name, is on the Cartridge/Properties tab, under “Variable name prefix”. You can set it be empty, if you want. Just don't complain when your cartridge's variables redefine major globals or clash with keywords. We suggest to use the var_ prefix to stay out of trouble.