See also the Subscription response object.

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

$subscription = $gateway->subscription()->find('a_subscription_id');

Otherwise, use Subscription::search().

If the subscription can't be found, you'll receive a Braintree\Exception\NotFound exception.

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.