KT2 jailbreak kt2 5.11.1.1 but cannot install KUAL

Hello! I am new to mobileread forum.
I want to jailbreak my KT2 running firmware 5.11.1.1
I find this thread from google, it seems that I can jailbreak using serial jailbreak.
I follow this tutorial
I do part 1-4 successfully.
I see the word **** JAILBREAK **** appear at the bottom of my KT2.
And this is the message from putty:
============================
Welcome to Kindle!

kindle login: root
#################################################
# N O T I C E * N O T I C E * N O T I C E #
#################################################
Rootfs is mounted read-only. Invoke mntroot rw to
switch back to a writable rootfs.
#################################################
[root@kindle root]# cd /mnt/us
[root@kindle us]# sh jb.sh
info jb_install:mount_root_rw:: Mounting rootfs rw
info jb_install:install_update_key:: Copying the jailbreak updater key
info jb_install:install_fw54_exec_userstore_flag:: Creating the userstore exec flag file
info jb_install:install_bridge:: Installing the jailbreak bridge
info jb_install:install:: Setting up MKK persistent copy
info jb_install:install:: Setting up RP persistent copy
update_to_display: update_mode=PARTIAL, wave_mode=257 inverted=0
[root@kindle us]# reboot
reboot: command arguments: no_sync=0, force=0, poweroff=0, exit_only=0, args=77072


[root@kindle us]# Broadcast message from root@kindle
(/dev/ttymxc0) at 0:07 ...

The system is going down for reboot NOW!
============================

So I believe I jailbreak my KT2 successfully.
I try to install KUAL following the part 5 but fail.
I download the latest KUAL package KUAL-v2.7.20-gc2948b8-20190604.tar.xz from this download thread
I put the file KUAL-KDK-2.0.azw2 into the Documents directory of my KT2.
However, I cannot see the Kindle Launcher after restarted.
I know this message is quite long. But I really need help!
Can anybody help me? Thanks!