I'm working in an e-commerce iPhone app which uses Magento SOAP api. When using the app, a user makes the payment with Paypal. For this I have integrated the paypal iOS sdk. After the user has made the payment using paypal, it returns a transaction id. My question is how do I update Magento about a successful paypal transaction. In the Magento store admin dashboard, the orders have "Pending Payment" status and blank "Last Transaction ID". What approach should I take to update them?