(a) Under the section "Payment Gateway Options", select Order processing via "VeriSign PayFlow Pro". Click on the "Update Store" button at the bottom of the screen to move to the next step
(b) In the next screen, select your payment options as shown in the screenshot below.
(c) Now enter your VeriSign login, Partner ID and the password.
Click on the "Finish Setup" button at the bottom of your screen when you are done.