Create webhook lookup

Creates a webhook lookup. A webhook lookup ties the API caller's REST API app to the subject account (or, if no subject is specified, to the API caller's account). If a webhook event is generated for an event that is tied to the account but not to a particular REST API app (for example, payments initiated with the NVP/SOAP APIs or through the user interface on PayPal.com), those webhook events will treated as if they were intended for the REST API app registered in the webhook lookup instead. Webhook events will then be delivered to any webhooks registered to that REST API app.