I have registration set up exhibition vendors. No shipping charges involved. (http://www.strollingoftheheifers.com/slow-living-expo-registration/#form) But on the same site I also have a merchandise store, for which shipping is set up on PayPal. So on the exhibition vendor form, I need PayPal to charge zero shipping. I have tried adding a shipping field to the form with a single value of zero, but this is not being transmitted to PayPal. How can I force zero shipping on PayPal in this situation?