If a user requires a PIN and pre-approval is setup, we need to show a UI component that allows the user to enter a 4-8 character PIN. It can only be digits, so let's validate it in JS. This is then passed through to the pre-approval AJAX call. There is no specific error that says the PIN is bad, so I think in our flow, the Paypal call will fail and we'll fall back to non pre approval.