Maybe it could be possible to manually extract the 12-digit code from the 36-digit one. A too simple example: have you tried to check if the 36 digits divided into 3 groups work?
2501000E0900 13009C030490 330691452269
Related topics
https://community.zyxel.com/en/discussion/13070/dx5401-aten-atse
2501000E0900 13009C030490 330691452269
Related topics
https://community.zyxel.com/en/discussion/13070/dx5401-aten-atse