Paypal Invoicing API
So how to get your paypal invoicing set up? Login to the Paypal Sandbox with the account associated to your Paypal Invoicing Application (Google that, to find the latest URL!!) Click My Apps, create a new APP, save as draft and you will be ready to start testing. Note that when you are testing the Sandbox App Id is always APP-80W284485P519543T and the end point is https://svcs.sandbox.paypal.com/. You'll need approval from Paypal when finished testing!