code: public Subscription changeAmountTemporary( Subscription subscription, Integer amount ) {
      return changeAmount( subscription, amount, 0, null, null );
    }
docs: Changes the amount of a subscription.<br>
  <br>
  The new amount is valid one-time only after which the original subscription amount will be charged again. If you
  want to permanently change the amount use {@link SubscriptionService#changeAmount(String, Integer)}
  .
  @param subscription the subscription.
  @param amount the new amount.
  @return the updated subscription.