-- Starting switch on '3002@black-0' to 94821182
    -- Executing Dial("USTM/3002@black-0", "Zap/1-1/4821182") in new stack
Mar 19 15:30:57 NOTICE[599]: app_dial.c:1059 dial_exec_full: Unable to create channel of type 'Zap' (cause 0 - Unknown)
  == Everyone is busy/congested at this time (1:0/0/1)
    -- Executing Congestion("USTM/3002@black-0", "") in new stack


 Same error from all working SIP devices/channels as well.