Dear user,
Unfortunately, the MTU serial number cannot be seen by LMT, however it can be queried via SSH.
You can connect by PuTTY to the IP of the PBX to port 22.
The passwords are the default (Change_Me) and must be enabled in the PBX web interface.
Remember that the 'serial number' of the MTU is known as the BOM CODE item if we see it on the command line.
I'll leave you an example of how the query should be done:
log in as: admin
password: Change_Me
>enable
Password: Change_Me
#super
Password: Change_Me
$display elabel

Regards!