Please see the screenshot here:
http://ancestraldevelopment.jeffrygerbermd.com/wp-content/uploads/2015/07/pay-pal-button-settings.png
When you land on the paypal page, and click on the "No PayPal account? Pay using your credit or debit card", that is when the next screen gives you this message: "The link you have used to enter the PayPal system is invalid. Please review the link and try again."
Why wont it let me proceed to finish the transaction in sandbox mode?