Unable to parse M3U file

You start telly, and see something like this:

INFO[2020-05-29T16:08:59Z] telly is preparing to go live (version=1.1.0.6, branch=dev, revision=741108cd2100cf9f4d3a13f771d1ebe5132baae6)
INFO[2020-05-29T16:08:59Z] Loading M3U from http://wherever/it/might/be/channels.m3u
ERRO[2020-05-29T16:08:59Z] unable to parse m3u file                      error="malformed M3U provided"
ERRO[2020-05-29T16:08:59Z] error when preparing provider                 error="malformed M3U provided"
ERRO[2020-05-29T16:08:59Z] error when processing provider                error="malformed M3U provided"
INFO[2020-05-29T16:08:59Z] telly is live and on the air!
INFO[2020-05-29T16:08:59Z] Broadcasting from http://0.0.0.0:6077/
INFO[2020-05-29T16:08:59Z] EPG URL: http://0.0.0.0:6077/epg.xml

The single most common cause of this is that you haven't changed the default filter in the config file, or you're configuring a filter on tags that don't exist in your m3u.

If it's not that, verify that your M3U meets telly's expectations.