mapdev\FacebookMessenger\Messages\StickerMessage::toArray PHP Method

    public function toArray()
    {
        $this->checkRecipient();
        if (is_null($this->sticker)) {
            throw CouldNotCreateMessage::noStickerDefined();
        }
        return ['recipient' => ['id' => $this->recipient_id], 'sticker_id' => $this->sticker];
    }