Whenever American Truck Simulator or Euro Truck Simulator 2 is updated by SCS you will need to downgrade your game until TruckersMP pushes an update to support the new version.
Updating TruckersMP to the new version may take some time, we also do not have an average waiting time for the new updates. Once we support the newest version, it will be posted on our socials and our Discord.
To upgrade/downgrade ATS or ETS 2 you need to open Steam. After doing that follow these steps:
You can also watch this video on how to downgrade your game.Video
Open your Library
Right-click on ATS / ETS 2
Head over to Betas
=> Here you need to find the correct version. If TruckersMP is fully updated and supports the new version, you need to select "NONE - Opt out of all beta programs".
For ATS select: NONE - Opt out of all beta programs
For ETS2 select: NONE - Opt out of all beta programs
If you still have this issue please check this post and follow these steps.
TruckersMP - Support