/etc/zaptel.conf

span=4,1,0,esf,b8zs
bchan=73-95
dchan=96

/etc/asterisk/zapata.conf

switchtype=national
signalling=pri_net
usecallerid=yes
callerid=asreceived
echocancel=yes
echocancelwhenbridged=yes
echotraining=yes
rxgain=0.0
txgain=0.0
relaxdtmf=yes
language=en
context=fax

group = 3
channel => 72-95

Dial command from /etc/asterisk/extensions.conf

[fax]
exten => _8017037015,1,Dial(Zap/g3/${EXTEN})

error

slk-aloc-01*CLI> dial 8017037015@fax
    -- Executing Dial("OSS/dsp", "Zap/g3/8017037015") in new stack
Dec 20 21:53:24 NOTICE[20478]: app_dial.c:1049 dial_exec_full: Unable to create channel of type 'Zap' (cause 0 - Unknown)
  == Everyone is busy/congested at this time (1:0/0/1)
slk-aloc-01*CLI>