Amazon and Ebay Webservices

We need Amazon and Ebay/Paypal webservices based application. So basically this application will run in the cloud. It will register with Amazon developer services and once it registers, it will be able to access our multiple Amazon accounts. Same goes for Ebay and Paypal. This app must register with Ebay as a developer app so ebay allow our app to access client's or our ebay seller accounts and same goes for paypal. Following are the functions we need to be able to achieve. 1. Cancel an existing order based on reference number. In case of Amazon, just cancel the order if it is not processed yet. In case of ebay, need to make refund from paypal. That means, app should be able to access the paypal and do the refund if the order is cancelled and then use ebay API and send the order cancellation request to customer. 2. Make full refund or partial refund on an order based on reference number. In case of Amazon it is straight forward. Either it is full or partial refund. But in case of ebay/paypal, we get an option weather we also want to cancel the ebay transaction while doing this refund in paypal or we don't cancel the transaction but just do the refund. 3. Download transaction details related to an order number 4. Update new tracking ID on an existing processed or shipped order in Amazon or ebay seller account In other words, we have to make sure that our app is registered with Amazon and ebay and paypal so other users also able to use our app and this app can access their accounts. We don't really need a fancy front end interface. Just a basic interface is enough as we will later integrate the code with our existing app that we already building. Thanks Sunny