@KuroYami 

Bring Satellite Deco to the room where Main Deco is, power on Satellite Deco and do not connect it with Ethernet cable. The purpose of this is to check if Satellite Deco will connect to Main Deco over WiFi.

If it does, Satellite M5 LED goes green and after some time Satellite Deco appears in Deco app as online, open Satellite Deco info page in Deco app and see how it is connected, example:

If you see (2.4GHz/5 GHz) after "Connected to:" like it is in above example, it means Satellite Deco WiFi hardware works just fine.

  @Alexandre. 

Thank you for your reply.

Yes I did that too. I reset the slave and reconnected it to main just fine via wifi. But when I moved it upstairs, its still green but upstairs' wifi just doesn't have internet. SMB works fine.

When I turned off the slave deco, and all device connected to main, it works. Which is my current situation for now.

  @David-TP 

Hi,

Yes I did checked on the IP address. It is within range. Only my NAS is static, all other devices are dynamic.

When the slave becomes main "slave-main", i did not connect the old main to slave as the "slave-main" 's WLAN doesn't have internet access. So I don't think I'll need to continue adding old main as slave.

Lastly, thank you for everyone's replies, really appreciate it. Anyways, I just ordered a BE65. old m5 main will be slave at the car porch and the old m5 slave will handle LAN connections in my other room with a switch.