1. I changed to $url = "https://www.sandbox.paypal.com/cgi-bin/webscr"; in vm>paypal>config .
2. I changed PayPal payment email: to my sandbox Seller account email.
Now how do I use sandbox Buyer account to pay for a product using credit card? I tried to enter the Buyer account email in user email but Joomla shows invalid email address. How do u do it?
What about "Name On Card:", "Credit Card Security Code:"? Sandbox Buyer account doesn't generate these.
I couldn't figure out why Joomla choked on that; so I just used another of my email addresses there; it makes no difference to the process, you can log in to PayPal with the Sandbox buyer account anyway and then check the PayPal emails ok.