PAN - Migrate client from pand to bluez5

Hi all,
currently I have a Bluetooth PAN working where both the master and 
clients run on outdated software, i.e. it uses bluez3/4 tools (hcitool, 
hciconfig, pand, etc).

I'm attempting to gradually migrate (unfortunately I can't touch the 
server for the time being) this setup by replacing some of clients with 
new hardware that runs Ubuntu 20.04 (bluez 5.53). I've been attempting 
to establish a connection with the master (pand 4.59, GN role) following 
a guide that I think describes the most up-to-date methodology, 
http://blog.fraggod.net/2015/03/28/bluetooth-pan-network-setup-with-bluez-5x.html. 
  Unfortunately, I can't even get past the pairing step, it ask for a 
PIN that was never needed before, and it gets canceled right after:

[bluetooth]# agent on
[bluetooth]# power on
[bluetooth]# scan on
[bluetooth]# pair XX:XX:XX:XX:XX:XX
Attempting to pair with XX:XX:XX:XX:XX:XX
[CHG] Device XX:XX:XX:XX:XX:XX Connected: yes
Request PIN code
[agent] Enter PIN code: Request canceled
Failed to pair: org.bluez.Error.AuthenticationCanceled
[CHG] Device XX:XX:XX:XX:XX:XX Connected: no

With the old setup no PIN was needed. I've searching if it is possible 
to pair without PIN, or what indicates that a PIN is necessary but with 
no avail.  I've tried to use another agent like "DisplayOnly" or 
"NoInputNoOutput", but the PIN is always requested.

Why is a PIN now needed? What am I missing?

Any help is appreciated. Thanks.