Pro Sites: Pay Pal IPN and Sandbox

Maybe this will save someone a headache.

When you test your IPN in the paypal sandbox, make sure that you have pro sites set to Test Mode (Sandbox) or it won't work. Sounds obvious but I spent way to much time over thinking this one today.

The error the IPN tester will throw is
"IPN delivery failed. HTTP error code 503: Service Unavailable "