There is a problem in dfu_boot script in lpcscrypt under linux. the version is installed via LinkServer_1.6.133.x86_64.deb.bin
My installed dfu-util is 0.11
whose output is following
dfu-util 0.11
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2021 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/
Found DFU: [1fc9:000c] ver=0100, devnum=115, cfg=1, intf=0, path="3-1", alt=0, name="DFU", serial="ABCD"
but vp_hex generated is not corrected:

cause here DEVICE_VID_PID is 0x1f9c:0x000c

Which prevents from detecting dfu mode