The installation of the Internet gateway does not succeed, you are stuck because you encounter the message: "No Internet-gateway has been detected".
Check that the gateway is properly plugged directly into a wall outlet. The LED lights up. If it does not light up, make sure that the socket works.
Make sure that you have installed the gateway within Wi-Fi range of your Box.
Ensure that the LED is blinking blue. If the LED is solid blue or if it is not lit, then you need to reset the gateway.