Twitcastinglive publishes live output next to finished uploads, and the two behave differently. A replay, VOD or clip has a settled file behind it and downloads normally. A stream that is still running does not have an end yet, so wait for the replay to appear before pasting the link. Twitcastinglive is handled by the media route, which reads the site's own rendition list before choosing anything. No credentials are involved anywhere in this path — neither yours nor ours.
Either paste a Twitcastinglive link above, or put tikt.com/ in front of any Twitcastinglive URL in your address bar:
tikt.com/https://www.example.com/path/to/media
What you actually have to do
1. Copy the Twitcastinglive link
Use the address bar or the platform's own share button — both give a URL the extractor recognises. Point it at the single item you want, not the page around it.
2. Let it read the renditions
Paste the URL above. The extractor asks Twitcastinglive which renditions exist for that item and picks the best progressive one rather than assuming a quality.
3. Save what comes back
The file arrives in the container Twitcastinglive served it in, and the extractor does not rebuild it — so what you end up with is what the uploader encoded, for better or worse.