Hi.

I've found that "Nextsong debug" is not working for liquidsoap accounts.

I have switched that on on my test account and nextsong.log file is not appearing in logs directory.

You most likely have a permissions issue of some sort preventing nextsong.log from being created in the log directory.  The "Nextsong debug" feature has no knowledge of which source is in use -- it's generated by the code in Centova Cast which chooses which track to play next.  That code is called identically by each third-party source (via an HTTP callback), so there's no way your choice of source could impact whether or not it works.