Locally the script works great and get success. However when testing with PayPal sandbox it does not send back to site or I get error about buyer and or seller. I entered the correct email information for my seller and my sandbox buyer. Do I need to setup and return address when sale complete at PayPal? If so which page would I be redirecting back to on my site?

Great script and can see many uses

Thank you for creating this.

> when testing with PayPal sandbox it does not send back to site

No, the script does not work with PayPal sandbox. PayPal sandbox uses fake email addresses and so the script can't send emails.