Forza Horizon 4 - PO Cars

I'm going to assume that "PO" is "pre-order", but regardless there aren't any restrictions on what cars you can/cannot put up for auction or buy at the auction. The only thing that would restrict that is if

your Privacy and Online Safety Settings were set to not allow you to use the Auction House in game.

yeah man every car is available in auction house you cant sell a car without using auction house it can be a pain if your selling multiple!!

All the cars that are available in the game can be sold or bought at the auction house.

if you go to the auction house, you should be able to list it there

Translation:

Forza Horizon 4 no pre-order car after upgrading Ultimate Edition

Hello, I played the Horizon 4 Standard Edition for two months with XGP at the end of 2019, purchased the Horizon 4 Ultimate Edition on January 1, 2020, and downloaded all the DLC, but did not receive the two cars I received after upgrading the Ultimate
Edition Pre-purchased cars (Benz AMG GT PO and Nissan GTR PO), I saw someone received in the forum a few days ago, can you solve or reissue, thank you.

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Answer:

Hi, you should find the two cars inside your messages in the menù. The cars should be in the "gift" tab and you need to directly download them from the message