I got it working. The requirements in my case were:
- Use the right GPON Serial Number: you can take that number it from your current router. In the case of the Zyxel AX7501 it was a bit hidden.
- The right PLOAM password: It is in the same place of the GPON serial number. It is the MAC address of the router without the : (colon) symbol in between the address.
- The right VLAN: Again from the router configuration settings, I could see mine was setup to use VLAN 10.
There was no need to clone the mac address of the router in the new router.