@ErlendLL 

This is something that should work. When it does, you should see Ethernet symbol.

Start with this document: General questions about Ethernet Backhaul feature on your Deco

See if you have compatible Ethernet switch. Those from D-Link brand usually not.

If document does not give you ideas of what is wrong in your setup, start with tracing. Suggested steps:

1. Bring Satellite Deco to Main Deco and connect it to Main Deco with short Ethernet cable. Verify Ethernet link;

2. Bring Satellite Deco to switch, unplug cable connecting switch to Main Deco, plug Satellite Deco to it. Verify Ethernet link;

3. Plug cable connecting switch to Main Deco back to the switch. Connect Satellite Deco to the switch with short Ethernet cable you used in Step 1. Verify Ethernet link;

I am thinking you've got an idea. Continue that way step by step, checking all cables, till Satellite Deco is in it's permanent place. The step where Ethernet link will not be established by Satellite Deco is the step where something is wrong with the cable.