public function verify()
    {
        $this->resetApiParameters();
        $this->setCommonApiParameters();

        $wrongKeys = array();
        foreach ($this->getApiKeys() as $key) {
            $this->setApiParameter('apikey', $key);
            try {
                $this->callApi(self::API_URL_VERIFY);
            } catch (RuntimeException $e) {
                $wrongKeys[] = $key;
            }
        }

        if (!empty($wrongKeys)) {
            throw new InvalidArgumentException(
                sprintf(
                    'Following API keys are invalid: %s',
                    var_export(implode(',', $wrongKeys), true)
                ),
                401
            );
        }

        return $this;
    }