[Ahrim]

And what does it do for now, if I may ask?

Try This.

Код:

CMD:tduty(playerid, params[])//Trucker-duty dialog
{
    new vehicleid = GetPlayerVehicleID(playerid);
    if(vehicleid == 403)
    {
    ShowPlayerDialog(playerid, 2, DIALOG_STYLE_LIST, "Choose a route.", "Blueberry Packaging.\nMainstreet Ammunation.\nFlint Food Factory.\nOff-duty (Removes the CP)", "Confirm", "Close list");
    }
    else return SendClientMessage(playerid, 0xE64D51FF, "[*]Message: You need to be in a truck with a trailer to use this command!");
    return 1;
}

You were trying to get the vehicle's model ID, not Vehicle's ID.