Imported Playlists are found under Music Library > Imported Playlists.  As long as they are in the share path, Sonos will import 2 types of playlists, iTunes and .m3u.  If yours are another format, convert them to .m3u.

After doing some house cleaning and eliminating duplicates, cleaning up the library, etc; one old, existing playlist is showing under ‘imported playlists’.  This particular playlist is a .wpl file.   I don’t know why it appeared but it works.  Last night I created a new playlist but it does not show under ‘imported playlists’.  

Is there a procedure, like indexing, that will discover the playlist and list it under imported playlists?

Also, the support section of Sonos seems to indicate that a playlist created with Windows Media Player (.wpl) is acceptable.

So, I ran an index and the new playlist is there under ‘imported playlists’.  So for the time being all is well.