3403D diagnostic code

Hey there, Mauro.

Welcome to the Apple Support Communities! Thanks for your post about the internet recovery error you are seeing. Maybe we can help.

Let's delve a little deeper. Are you using any sort of specialty network, such as a captive network, VPN, or any other network with a specialized configuration? More info about captive networks can be found in Use captive Wi-Fi networks on your iPhone, iPad, or iPod touch. If not, let's have you Reset NVRAM or PRAM on your Mac and try to complete the process once more. You might also try connecting to a different Wi-Fi network and attempting the setup as well.

Let us know if you see anything different when trying these steps.

Be well!