How can I approve a Purchase Order and how to Search only for Purchase Orders

Hello,

Hello I am developing an iPhone application that allows you to edit the values (unlike the official version). It has been going good so far, but I have 2 problems. I cannot approve a Purchase Order, I can edit any of the other fields but not the orderStatus as it fails. Here is my code in objective C and using wsdl2objc:

platformMsgs_UpdateRequest *update = [[platformMsgs_UpdateRequest alloc] init]; // Allocates the update request
tranPurch_PurchaseOrder *order = [self.orders objectAtIndex:indexPath.row]; //Gets the Purchase Order to be modified from UITableView
tranPurch_PurchaseOrder *updateOrder = [[tranPurch_PurchaseOrder alloc] init]; //Allocates a purchase order instance.