Internet recovery broken on Macbook Pro. Error message given is " apple.com/support -3403F ".
That indicates your machine can’t reach the internet.

Troubleshooting this will be challenging unless you have network / wire shark capabilities and can make sure the packets from this machine are going unhindered to Apple’s servers.

In practice, this is far easier to diagnose by using a second Mac on this network to see if it can boot to recovery. If not - you know it’s the network. If the second can boot - you have a hardware failure or network card failure on the problem Mac.

Taking the suspect Mac to another network that is known to be good (or just taking it to 4 or 5 networks and assuming one of them has to be OK) can also help you isolate if the problem is the network or the hardware.

Lastly, setting up a caching server on your local network would let you see those logs and be sure the Mac in question was requesting the correct recovery image from the internet. 


https://support.apple.com/guide/mac-help/manage-content-caching-on-mac-mchl3b6c3720/mac


Content caching is a super power move, since you only download one copy of each asset, then your local network accelerates all further installs and boots.