A local playlist can fail because it is incomplete, incorrectly formatted, saved with the wrong content or unsupported by the player. Inspect a private copy carefully before changing account credentials. A file extension alone does not establish that the contents are a valid channel list.
Check whether the download completed
Compare the file size and download result with the source’s documented information where available. A zero-byte file has no entries to import. A truncated file may show some channels and fail later, which is different from an account that never authenticated.
Preserve the original structure
Extended playlist metadata and media addresses depend on line structure. Copying through a formatted document or chat can wrap, remove or alter characters. Use a plain-text editor for an authorised local file and keep the original before attempting repairs.
Ask for a fresh supported source
If the source file itself is broken, a new password is not necessarily the remedy. Request the current playlist or supported account format through the established service channel. Do not send a private full file to a public validator just to obtain a syntax report.