Thank you for looking in to my issue. Actually my problem is I can't proceed from the Basic` setting menu.
I have installed the plugin and I can only see the "BASIC SETUP" tab in in the setting menu ( but i can see that there are lot of tabs in the Global settings menu https://usabilitydynamics.com/tutorials/wp-invoice/wp-invoice-settings-main/) and I dont have anyother settings.
Further When i tired to SAVE the Basic Setup by giving PAYPAL id and disable the "CREDIT CARD" option and fill out the other fields.. its not saving and RELOAD the same basic setup page in the "WP-Invoice First-Use Setup" again and again. Please help me on this ( i don't know how to upload screenshot here. if you can give me support email address ill mail you.