Hi Daniele,
the problem is that Legrand is not working if the router has active ipv4 and ipv6. They told to ask sunrise to disable ipv6. We already tested at home with Swisscom and the Legrand Solution is working as expected.
They cannot change their system to work only in ipv4 even if the router can give both.
Thanks for your understanding and support.
Regards
Gianpaolo