Hello @Dehyde 

If you would like to connect range extender to the router through Ethernet cable, please set up RE in AP mode as guide below , which will transform the wired network to a wireless one: How to connect TP-Link Wi-fi Extender to Router with Ethernet Cable (Access Point Mode）

If possible, it is recommended to use one type of network expansion device in the network, use either Range extender/ Powerline kit. For example, you may consider one more Wireless powerline unit to extend wifi network in the same housepowerlkine circuit/ under the same power meter