How to add to or alter you Google Checkout Preferences:
1) Go to google.com/checkout and sign in.
2) Click on "My Sales".
3) a. Click on Settings.
b. Click on Preferences.
c. Make sure that "Automatically authorize CHARGE..." is selected, otherwise it will wait to confirm the charge from your customer/client; and if they do not respond within 7 days, you will have to make them another invoice.
d. Check this box to receive an email about the transaction.
e. Click on "Save preferences".