I cannot access the internet after configuring my Mesh network, why?

There are several reasons why you cannot access internet after configuring your Mesh Network:

The RJ45 cable is not properly connected to the internet box or the main Mesh or in the wrong port.
The internet connexion from the internet box is not working properly.
The main Mesh did not succeed to retrieve the network informations of the internet box.
The Mesh units are not paired together.