Hi there,
The error is due to using the caravan. The caravan is only allowed to be towed by the car and if you try to tow it with a truck this error occurs.
This comes under Section 5 of https://truckersmp.com/rules
§5.1 - Server Auto Kicks
Ping - If your ping is over 600ms to the server, you will be disconnected from the server in order to avoid desync issues for others. This ping check is taken as an average.
Away from keyboard - Being inactive for over 10 minutes.
Car with trailer - Attaching a trailer to your car (not including the caravan.)
Truck with caravan - Attaching the caravan to your truck.
Headlights - Headlights must always be on between the hours of 21:00 (9 PM) - 05:00 (5 AM).
Unsupported accessories - Using police accessories or any other unsupported items (Special Cargo DLC trailers for ETS 2 and ATS).
Local Mods - Using local-only items such as sound and model accessories that use the /home directory (this does not include addon hookups).
Too many trailers - Using a modified trailer combination with more than 3 parts for ETS2 or 5 parts for ATS will cause the server to kick you, regardless of location on the map.
Negative cargo mass - Using a trailer with a mass lower than 0.
Mixing vehicle items - Using car parts on a truck, truck parts on a trailer or car parts on a trailer, and vice versa for each case.
I hope this helps.
Cheers,
Jake