[refshal]

I think that you have forgotten a return 1;

pawn Код:

public OnPlayerCommandText(playerid, cmdtext[])
{
if (strcmp("/start", cmdtext, true, 6) == 0)
{
if(IsPlayerInVehicle(playerid, 574))
SetPlayerCheckpoint(playerid, -147.1910, 1146.1820, 19.5938, 3.0);
return 1;
}
return 0;
}

Try that.