See also the Subscription response object.

If you want to look up a single subscription using its ID, use the subscription.find() method.

gateway.subscription.find("aSubscriptionId", function (err, result) {

Otherwise, use

If the subscription can't be found, it will return a notFoundError.

subscriptionId required, String

The value used to identify a specific subscription. If you do not specify an ID when creating a subscription, the gateway will generate a 6- or 7-character alphanumeric ID. When updating a subscription, you can only use tokens associated with the same customer that the subscription is currently associated with. Once canceled, a subscription can't be edited or reactivated. You must create a new subscription.