The notification kind, returned by calling
kind on the notification object, reveals what triggered the webhook. The
webhook_notification.kind for Payment Method webhooks will be one of the following:
The following table describes the conditions that trigger each kind of webhook.
A payment instrument that was previously enabled has been revoked by the customer.
A value representing an existing customer stored in your Vault. Use
Customer.find() call to look up a single customer.
PaymentMethod object associated with the revoked payment method.