@DazCuz 

>I have tried both methods in the manual to connect but I do not have a stable connections. 

What are these methods, can you explain? It is not clear from your post what do you mean.

Also, to where is your  desktop PC wired: TP-Link switch TL SG116 or to 2nd Deco X60?

  @Alexandre. 
Apologies. After I posted I thought it was short of info. 
I have Fibre to the curb NBN internet - FTTC - 

IPOE

Modem - Arcayden Telstra Smart Modem 3. 

I have tried to connect the main X60 between the modem and the switch. - Ethernet to desktop lag and sometimes time out. 
I have tried to connect the Main X60 to the switch - Ethernet to desktop lag and sometimes time out. 

I have tried to connect the Main X60 to the Modem/router -  Ethernet to desktop lag and sometimes time out. 
 

Cables have been checked. 
 

The only thing through the app with the setup is it doesn't have a choice for IPOE. I use the dynamic settings. 
 

I have also tried the IPTV settings and used the Australian NBN choice. 
 

Hope this is a bit clearer. 
 

Thanks. 
 

  @DazCuz 

I googled your modem name and got this picture:

Is this your modem? If it is, keep it running in its default modem/router configuration and instead reconfigure Deco mesh to run in Access Point mode: How to set up Deco to work in Access Point mode

  @Alexandre. 
Yes that's the modem. 
Thanks so much. I will give it a go and let you know how it goes. 

  @DazCuz 

Hi. 
I followed your instructions and connected the main X60 to the switch and put it in AP mode. 

I then added the 2nd X60. I connected this to a Ethernet cable to the switch for backhaul. 

The app says there is no Ethernet backhaul just wifi. 
 

The computer was working perfectly without the X60's connected and now that they are connected it is lagging again. 
 

Any help would be appreciated. 
 

Thanks

  @DazCuz 

It is possible either switch or modem is not compatible with Deco Ethernet backhaul protocol, or Satellite Deco does not like something about Ethernet cables you use. Let's find out.

Keep Deco mesh in Access Point mode.

Please do the following tests: 

1. Power off X60s. Connect Main Deco directly to modem/router with short Ethernet cable. Power it on. Wait till it is fully online. Connect Satellite X60 to different modem/router Ethernet port with short Ethernet cable. Power Satellite X60 on and wait till it is fully online.

Does Satellite X60 report Ethernet backhaul?

2. If it does, using same Ethernet cables connect your Deco with Ethernet cables the following way:

modem / Deco X60 router / 2nd Deco X60

Does Satellite X60 report Ethernet backhaul?

3. If it does, bring TP-Link switch TL SG116 to where your modem/router and Decos are, and using short Ethernet cables connect them as you did before:

modem / Deco X60 router / TP-Link switch TL SG116 / 2nd Deco X60

Does Satellite X60 report Ethernet backhaul?

4. If it does not, the last test will be to connect again Main Deco directly to modem/router with short Ethernet cable, and switch - to different Ethernet port:

modem / Deco X60 router

modem / TP-Link switch TL SG116 / 2nd Deco X60

Does Satellite X60 report Ethernet backhaul?

  @Alexandre. 
Thanks for all your help Alexndre. 
 

I finally got it going set up as an AP's with Ethernet backhaul. 
 

This is what I did. 

I turned off the isp modem/router wifi. 
 

I connected the main X60 by Ethernet directly to the router on the modem. 

I went through the setup on the app and set the main X60 as an AP.   Then I connected the 2nd X60 with wifi backhaul. 
 

I then connected my 2nd X60 to the modem/router port by Ethernet.  
 

I could see the Ethernet backhaul on the app. 

I finally have 2 access points with backhaul. The modem/router sets all the addresses. 
 

The internet on my PC isn't lagging anymore. 
 

Starting out this was far from how I thought I would have the mesh wifi up and running but it is working now so I am happy. 
 

Thanks again.