Why? Obviously Stellantis decided to restrict it. Only option is to try to register.
What it says on
https://www.converters-and-stellantis.com/signin
Is:
--- Welcome to the US & Canada Upfitter's Portal ---
This site is designed to be a technical resource for body builder's, second stage manufacturers,
and anyone doing business in the comercial upfit industry.
(like how they misspelled commercial)
It's been hit or miss for some. I think
@Jimmy07 had several failed attempts. I assume he got registered at some point?
I created an account no problem using my corporate email and just changed some details like my personal email after they granted access. Since my employer is in the IT space, I just made up some "electronics research and integration" BS for the justification.