code: public Subscription postponeSubscription(final Subscription subscription, final DateTime renewaldate) {
          return doPUT(Subscription.SUBSCRIPTION_RESOURCE + "/" + subscription.getUuid() + "/postpone?next_renewal_date=" + renewaldate,
                       subscription, Subscription.class);
      }
docs: Postpone a subscription
  <p>
  postpone a subscription, setting a new renewal date.
  
  @param subscription Subscription object
  @return Subscription