Error gateway response

I have a question about the process of the payment using a gateway emerchant. I have to provide all the variables to the gateway and get the answer if the charge was made. I can make the charge if all the data is correct, but i don't know how to receive the answer from the gateway, the manual give me a clue, the answer will provide in the variable "urlBack". Do you know how to get data from this gateway?

First I process all date in javascript then I send the information using the following code, but the answer I will receive in another page (https://acmax.mx/popup_2). All works very well but I have problems with the answer from the gateway.

Thank so much

    <form name="myPayTC" id="myPayTC" method="post" action="https://www.procom.prosa.com.mx/eMerchant/7727222_acmaxdemexico.jsp" onload='javascript:MyFrmOnLoad();'>

    <input type="hidden" id="total" name="total" value='total'>
    <input type="hidden" id="currency" name="currency" value="484">
    <input type="hidden" id="address" name="address" value="ACMAX">
    <input type="hidden" id="order_id" name="order_id" value='order_id'>
    <input type="hidden" id="merchant" name="merchant" value="7727222">
    <input type="hidden" id="store" name="store" value="1234">
    <input type="hidden" id="term" name="term" value="001">
    <input type="hidden" id="digest" name="digest" value='valDigest'>
    <input type="hidden" id="return_target" name="return_target" value="N/A">
    <!--<input type="hidden" id="urlBack" name="urlBack" value="https://acmax.mx/index.php?controller=ComercioResp">-->
    <!--<input type="hidden" id="urlBack" name="urlBack" value="https://acmax.mx/es/checkout/confirm">-->
    <input type="hidden" id="urlBack" name="urlBack" value="https://acmax.mx/popup_2">
    <!--<input type="hidden" id="urlBack" name="urlBack" value="http://acmax.mx/es/checkout/paymentmethod">-->

    <p><img src="https://acmax.mx/themes/theme674/img//bankwire.jpg" alt="Pago por tarjeta de cr&eacute;dito/d&eacute;bito" width="86" height="54" />&nbsp;&nbsp;&nbsp;&nbsp;<input type="submit" name="pButton" value="Pago con Tarjeta de Cr&eacute;dito/D&eacute;bito" class="exclusive" style="font-size:14px; height:28px;"></p>

    </form>

The code that has the server is the following:

    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <HTML version="-//W3C//DTD HTML 4.01 Transitional//EN">
    <HEAD>
    <TITLE>Verificacion de Compra</TITLE>
    <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1">
    </HEAD>
    <BODY>
    <form id="formars" name="formars" action="https://acmax.mx/popup_2" method="post">
    <input type="Hidden" name="EM_Response" value="denied">
    <input type="Hidden" name="EM_Total" value="102">
    <input type="Hidden" name="EM_OrderID" value="625">
    <input type="Hidden" name="EM_Merchant" value="7727222">
    <input type="Hidden" name="EM_Store" value="1234">
    <input type="Hidden" name="EM_Term" value="001">
    <input type="Hidden" name="EM_RefNum" value="initialrefnum">
    <input type="Hidden" name="EM_Auth" value="000000">
    <input type="Hidden" name="EM_Digest" value="initialdigest">

    <input type="Hidden" name="cc_number" value="0565">
    <input type="Hidden" name="total" value="102">
    <input type="Hidden" name="order_id" value="625">
    <input type="Hidden" name="merchant" value="7727222">
    <input type="Hidden" name="tx_id" value="322307f91ef2b5318e5d720f49fb30dace2ca474">


            <input name="pButton" value="Pago con Tarjeta de CrÃ©dito/DÃ©bito" type="Hidden" />

            <input name="address" value="ACMAX" type="Hidden" />

    </form>
    <script type="text/javascript">
    var formars = document.getElementById('formars');
    formars.submit();

    </script>
    </BODY>

    </HTML>

I can't change this code, so I need to get the data from the form "formars"

Solution

Well, for example, if you have set the urlBack parameter to some php page, let's call it returnCall.php.

Now, if the payment gateway is sending back the following 'post' data:

name1=cat&name2=dog&name3=echidna

Then in your php page, you can read that data as follows:

<?php
   $value1 = $_POST["name1"];
   $value2 = $_POST["name2"];
   $value3 = $_POST["name3"];
?>

<p>
    <ul>
        <li>Value1 = <?=$value1?></li>
        <li>Value2 = <?=$value2?></li>
        <li>Value3 = <?=$value3?></li>
    </ul>
</p>

Then the output on the page would translate to:

<p>
    <ul>
        <li>Value1 = cat</li>
        <li>Value2 = dog</li>
        <li>Value3 = echidna</li>
    </ul>
</p>

You could similarly have an aspx page that could do the same thing.

string Value1;
string Value2;
string Value3;

protected void Page_Load(object sender, EventArgs e)
{
    Value1 = Request.Form["name1"];
    Value2 = Request.Form["name2"];
    Value3 = Request.Form["name3"];
}