Adds three optional fields to the Subscription entity of the Subscriptions API
All these new fields provide more details about errors which may occur during a subscription's recurrence. If there are no errors, the values are null.
last_failure_codefield provides a unique code. This code may help to identify the type of the error, and this field may be used for localization purposes.
last_failure_detailsfield provides default error messages which may be displayed. Each failure code has its own error message.
last_failure_reasonfield provides the reason of failure (gateway/inventory/etc).