uncomment the Flow control commands from the /etc/hylax/etc/config.ttyPSxx file then restart the Hylafax device.

example class2:

# Modem-related stuff: should reflect modem command interface
# and hardware connection/cabling (e.g. flow control).
#
ModemType: Class2 # use class 2 interface
ModemRate: 19200
ModemFlowControl: xonxoff # default
ModemWaitForConnect: yes # wait for CONNECT on answer
#
#ModemResetCmds: AT&F2 # what you want for a Supra
ModemNoFlowCmd: AT&K # disable flow control cmd
ModemHardFlowCmd: AT&K3 # hardware flow control cmd
ModemSoftFlowCmd: AT&K4 # software flow control cmd
ModemSetupDTRCmd: AT&D3 # DTR off causes modem to reset
ModemSetupDCDCmd: AT&C1 # DCD follows carrier
ModemSetupAACmd: AT+FCLASS=0;+FAA=1 # enable in class 0

example class1:

# Modem-related stuff: should reflect modem command interface
# and hardware connection/cabling (e.g. flow control).
#
ModemType: Class1 # use this to supply a hint
ModemRate: 19200 # rate for DCE-DTE communication
ModemFlowControl: xonxoff # XON/XOFF flow control assumed
#
ModemSetupDTRCmd: AT&D2 # setup so DTR drop resets modem
ModemSetupDCDCmd: AT&C1 # setup so DCD follows carrier