I have a mesh AC1200 system DECO S4R. I've lost the signal to the garden as we've extended  and there's an extra wall for the to travel through. I've added Whole House Mesh Add on Unit DECO M3W. The new M3W plug shows on the DECO app but nothing seems to automatically connect to it. I've tried pluging it into the garage (half way to the end of the garden) but it does not work as a relay. All DECO units( 1 router DECO, 2 extra units and the new plug M3W) connect directly  to the router rather than connecting to each other to sebd the signal further. Should I be able to use the M3W as a staging post, relying the signal down the garden? If not is it worth buying another DECO to relay the signal? Or is it that the distance from the router DECO to the end of the garden is too far for this system?Thank you for your help.