When using PayPal (no matter which integration I think), we sometimes get the following error:
PAYPAL GATEWAY HAS REJECTED REQUEST. THE FIELD SHIPPING ADDRESS STATE IS REQUIRED (#10729: SHIPPING ADDRESS STATE EMPTY).
This was already the case for China and Japan. So we added these countries to the list of countries where the state is required (under System - Configuration - General). But for which countries does PayPal also require the state field? I guess there are more. We also asked the PayPal merchant support, but they could not give us any information (screw you, guys!). Maybe someone else has a complete list or we can build up one together?