Did you put the log out password into your tamagotchi? If you didn't, that is the problem. But if you did then you get the money automatically so you don't have to worry about a money code.
First, enter in your password and username. Then DO NOT TOUCH ANYTHING on your Tama until you get the password from logging out. Input the password and yo will get all your money. The max you can get in one login is 9900 (I've been there ^^)