TruckersMP does not support the latest game version of Euro Truck Simulator 2 or American Truck Simulator yet.
Check out the following guide on how to downgrade so you can keep playing on multiplayer:
How to downgrade
Members must be 14+
Members must have a working Microphone
Members must have an active Discord account
Members must not be part of another VTC
Members must be active on VTLOG
Members must be registered on this VTC Page.
Members under the age of 14 MAY be considered, depending on maturity.