I would recommend going to Setup>>Customise Form>>Invoices>>Selecting the layout and form before selecting Customise. This will show you the customise form i.e. the way in which it is printed/emailed you can then ensure that you have correct fields listed for your requirements. Help Article: Personalising forms ( http://help.myob.com/wiki/x/7YBW ) would be able to assist with that process in more detail.
If you do require further assistance with producing your invoices or have further enquires you more than welcome to post on the MYOB Community Forum http://community.myob.com/ I’m sure the MYOB Community would be happy to assist.