There are many reasons that cause your failed to download:
The videos are private, deleted, or limited only to 1 country
Your download links are not the TikTok video links. Link example:
https://vt.tiktok.com/ZSJmdax66/
https://www.tiktok.com/@tutuguy543/video/6965496459718380806
https://m.tiktok.com/v/6969576366555598085.html
https://v.douyin.com/3vn57r/