[wups]

pawn Код:

if(!strcmp(cmdtext, "/killall", true))
    {
        KillAll;
        return 1;
       
    }
if(!strcmp(cmdtext, "/vehiclename", true))
    {
        new vehicle = GetVehicleNameByModel(432);
        new string[125];
        format(string, sizeof(string), "You are currently sitting in a %s", vehicle);
        SendClientMessage(playerid, -1, string);
        return 1;
       
    }

Bad examples..
Function can't be writen like that(KickAll. You must use brackets ().
As for the vehicle name, you're storring it's name in to an integer.