[Plugin: WP-Invoice] Paypal Error

Hello,

I am getting the following error when testing.

Error:

“The link you have used to enter the PayPal system is invalid. Please review the link and try again”

All of my Paypal settings are correct:
username/account: correct.
Test Mode: No.
Paypal Button URL: Default that came with installation: https://www.paypal.com/en_US/i/btn/btn_xpressCheckout.gif

Any ideas how to solve this problem? Resources to turn too…

I like this mod, and would be interested in buying the premium version and some additional plugins, but need to see how it is going to all work first.

Guidance would be appreciated.