I would like some help to configure a wired ethernet backhaul.

ISP modem Huawei

Router AX73 fw 1.3.6 20240325

Extender RE505X fw 1.0.13 20230926

From ISP Modem I have 2 ethernet cat5e cables going to Router and Extender. 

1. Firts cable from ISP Modem Lan1 to wan port of Router AX73. It works fine and I have wifi working properly. 

2. Second cable from ISP Modem Lan2 to Lan port of RE505X extender. With this configuration I can configure extender as AP modem and have wifi working properly as well. But when I try to create a OneMesh Network but, via wired connection the Router is not able to find the Extender. I can only do it via wireless connection, but the speed is slow as both devices are not very close. Im not able to set a new cable from extender to Router due to physical limitations. 

Is there a way to configure a wired OneMeah Network with my setup? 

Do I need to configure any special route on the ISP modem to allow router and extender connection? How?

Thanks