paragraph1\phpFCM\Message::createTo PHP Method

    private function createTo(array &$jsonData)
    {
        switch ($this->recipientType) {
            case Topic::class:
                if (count($this->recipients) > 1) {
                    $topics = array_map(function (Topic $topic) {
                        return sprintf("'%s' in topics", $topic->getIdentifier());
                    }, $this->recipients);
                    $jsonData['condition'] = implode(' || ', $topics);
                    break;
                }
                $jsonData['to'] = sprintf('/topics/%s', current($this->recipients)->getIdentifier());
                break;
            default:
                if (count($this->recipients) === 1) {
                    $jsonData['to'] = current($this->recipients)->getIdentifier();
                } elseif (count($this->recipients) > 1) {
                    $jsonData['registration_ids'] = array();
                    foreach ($this->recipients as $recipient) {
                        $jsonData['registration_ids'][] = $recipient->getIdentifier();
                    }
                }
        }
    }