hello, @Arnoldpuan, can you get internet directly from the existing router? If so, you do not have to setup PPPoE on the Deco, instead, you can choose dynamic IP;

Usually we connect the Deco to a pure modem and set it up with the username and password given by ISP and enable VLAN ID if needed to make it work. 

You can give it a go by setting dynamic IP or connect the Deco to the modem directly, bypass the router and setup PPPoE.

May it help and have a nice day. 

Ho. Thanks for your advice. I have successfully setup my mesh Wi-Fi for my house. But I found that the primary mesh which I connect to router via LAN cable speed is fast, and the additional 2 mesh which I add on later, via wireless, the speed is slower. Is it normal. Cause the seller told me that, with this deco M9 plus, will able to get 2 5GHZ Wi-Fi. 1 will be from the router, and 1 will be for the mesh.

@Arnoldpuan 

It is normal that the speed is slower from the slave Deco than the main Deco due to the interference. But we need get to know what are the speeds you can get from them separately. 

You can move them closer to the main Deco or swap their locations to give it a go.

And the seller is right, there are 2 5GHz networks, one for the wireless connection, the other one for the wifi backhaul only. 

Good day.