If you're tech-savvy, you can host your own private bot to avoid the limitations or downtime of public ones. atex-ovi/DownloaderX - WhatsApp Bot - GitHub
Sometimes a video is “Not available in your country.” A bot’s server might be located in a region where the video is available, allowing the bot to download it and send it to you (Note: This exists in a legal gray area). Youtube Video Downloader Whatsapp Bot