2018 Macbook Pro not able to install Mojave

It's an added security measure. You can reinstall Mojave via internet restore

 

Why not remove the firmware password and then install Mojave?

 

You need to disable secure boot.

He will need to create an admin account on whatever software can be installed, boot into recovery, remove secure boot in the f/w security utility, then boot into USB.

 

Hold down: CMD+OPTION+R on boot to start up Internet Recovery.
If there is no image on the system or no local recovery to boot from then the only place you can boot is internet recovery.

Unless the system has "allow external boot" enabled; which it sounds like it doesn't.

 

Here is Apple's information about Secure Boot on a T2 machine:
https://support.apple.com/en-us/HT208330

 

OP wrote:
"So a customer brought in a 2018 Macbook Pro that he had wiped and wanted to do a fresh install of Mojave from a thumb drive. He has a firmware password on the laptop. Guess what? Not possible. The T2 chip blocks everything and requires another machine with a T2 chip to connect to it in order to make this happen."

Yes, that's the way it works now.

The solution is to take the laptop to a brick n mortar Apple Store genius bar, and they will "put it right".

WARNING!
Unless the customer has HIS ORIGINAL SALES RECEIPT, Apple WILL NOT do this for him.

In that case, he'd better start looking for a new laptop.
And... if it's a Mac laptop... he'd better be durned careful about what he does with it "next time"...