[Yuryfury]

Try this:

pawn Код:

public OnPlayerEnterCheckpoint(playerid)
{
    new vehicleid = GetPlayerVehicleID(playerid);
    if(IsPlayerInVehicle(playerid,vehicleid) && IsTrailerAttachedToVehicle(vehicleid))
    {

            SendClientMessage(playerid, 0xAFAFAFAA, "Congratulations!");
            GivePlayerMoney(playerid, 5000);
            DisablePlayerCheckpoint(playerid);
    }
    else
    {
            SendClientMessage(playerid, 0xAFAFAFAA, "You need a trailer.");
            DisablePlayerCheckpoint(playerid);
    }
    return 1;
}

This way the player has to be in the specified vehicle AND have the trailer attached.

Compiles with no errors