See also the Subscription response object.

If you want to look up a single subscription using its ID, use the Subscription: Find method.

Ruby 
subscription = gateway.subscription.find("a_subscription_id")

Otherwise, use Subscription: Search.

If the subscription can't be found, it will raise a Braintree::NotFoundError.

Arguments
subscription_id 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.