/**
  * @param \SubscribePro\Service\Subscription\SubscriptionInterface $subscription
  * @return \SubscribePro\Service\Subscription\SubscriptionInterface
  * @throws \SubscribePro\Exception\EntityInvalidDataException
  * @throws \SubscribePro\Exception\HttpException
  */
 public function saveSubscription(SubscriptionInterface $subscription)
 {
     if (!$subscription->isValid()) {
         throw new EntityInvalidDataException('Not all required fields are set.');
     }
     $url = $subscription->isNew() ? '/services/v2/subscription.json' : "/services/v2/subscriptions/{$subscription->getId()}.json";
     $response = $this->httpClient->post($url, [self::API_NAME_SUBSCRIPTION => $subscription->getFormData()]);
     return $this->retrieveItem($response, self::API_NAME_SUBSCRIPTION, $subscription);
 }