Hey Brogan the paypal email address in the business field matches the one I entered in the ACP.Check the paypal email address in the business field.
See this thread: http://xenforo.com/community/threads/user-account-upgrade-error-with-paypal.22283/#post-279659
Yes I am using the test users that were created from the sandbox.Request not validated means that PayPal didn't know of the details you sent through to it. Are you generating requests from the sandbox, using users that you created in it?
I haven't done anything with the sandbox since writing the initial code, but I did have it working then. If it doesn't work now, then maybe something has changed, but using the live PayPal site does work.