> the number 1023 does not work
Does not work? What do you mean: this numer is used par many customers every day, it works!
What is the result you get when dialing it (from another box that yours since it's not yet connected of course)
> my box has error code "etape 1/4" since yesterday
Here we are only customers like you.
So this kind of problem can only by solved by the official SFR customer service:
Digiclient NC → parti de sa planète disparue, pour une nouvelle terre d'accueil ♥LaBox THD 4K (V3) - Réseau FttB à 200↓↑20 Mbit/s