Sandbox mode – sales not completing

Thank you for creating and supporting this plugin – it really is a powerful and well designed tool.

I am setting up a new site with the free plugin and using sandbox mode to test everything out. I can get to the point where I pay in PayPal and it returns me to the site and resets the cart.

However, the transaction is never completed according to the WP Simple Cart log. It states that it has received the IPN from PayPal but not as a completed transaction. I do not receive any of the order confirmation emails (as the buyer) or order notification emails (as the seller).

Is this supposed to work in sandbox mode and I am doing something wrong?

Thank you

https://wordpress.org/plugins/wordpress-simple-paypal-shopping-cart/