A download can save an HTML error or login page under a playlist-looking filename. The player then receives web-page text instead of channel entries. Check the download response and source rather than assuming the file is valid because its name ends in .m3u.
Look at a private text preview
If the file opens with web-page markup or a message such as access denied, it is not the playlist you expected. Do not execute the file or upload it elsewhere. Keep any account-bearing address out of screenshots while documenting the result.
Consider authentication and redirects
The source may require a current account request or may have redirected to an error page. A browser’s saved-file name can hide that distinction. Ask the service for the supported retrieval method instead of repeatedly importing the same error document into different players.
Retest through the intended route
Once the source is corrected, obtain a fresh file and import it as a local playlist. Keep the old working configuration until the new import succeeds. A player reinstall cannot transform an HTML error response into a valid channel list.
