You still need to send minecraft the number of slots. This sets the values of Xms, Xmx and game_slots depending on what the client selected in the configurable option named "Ram"
<?php
include('default_values.php');
switch ($params["configoptions"]["Ram"])
{
case "1GB":
$billing_api_values["gamevar_Xms"] = "1024";
$billing_api_values["gamevar_Xmx"] = "1024";
$billing_api_values["game_slots"] = 8;
break;
case "2GB":
$billing_api_values["gamevar_Xms"] = "2048";
$billing_api_values["gamevar_Xmx"] = "2048";
$billing_api_values["game_slots"] = 16;
break;
}
?>