How to setup PayPal Standard Payment integration with PHP

PayPal Standard Payment 

I think you have already create business account in PayPal. And setup Instant Payment Notification Preferences

Here are simple method for "Instant Payment Notification Preferences" setup

Click on edit profile
1. Under ‘Selling Preferences’ >> ‘Instant Payment Notification Preferences’
a: Set the IPN value to ‘On’
b: Set the IPN URL "http://www.techsudhir.com/ipn.php"

HTML Payment Parameter

SIMPLE HTML FORM

//Set useful variables for paypal form
$paypalURL = 'https://www.sandbox.paypal.com/cgi-bin/webscr'; //Test PayPal API URL
//$paypalURL = 'https://www.paypal.com/cgi-bin/webscr'; //Live PayPal API URL
$paypalID = 'sales@techsudhir.com'; //Business Email

<form action="<?php echo $paypalURL; ?>" method="post">
<!-- Identify your business so that you can collect the payments. -->
<input type="hidden" name="business" value="<?php echo $paypalID; ?>">
<!-- Specify a Buy Now button. -->
<input type="hidden" name="cmd" value="_xclick">
<!-- Specify details about the item that buyers will purchase. -->
    <input type="hidden" name="item_name" value="Boat Ear Phone">
<input type="hidden" name="item_number" value="BEP32507725">
<input type="hidden" name="amount" value="35">
<input type="hidden" name="currency_code" value="USD">
<!-- Specify URLs -->
<input type='hidden' name='cancel_return' value='http://www.techsudhir.com/cancel.php'>
<input type='hidden' name='return' value='http://www.techsudhir.com/success.php'>
<input type='hidden' name='notify_url' value='http://www.techsudhir.com/ipn.php'>
<!-- Display the payment button. -->
<input type="image" name="submit" border="0"
src="https://www.paypalobjects.com/en_US/i/btn/btn_buynow_LG.gif" alt="PayPal - The safer, easier way to pay online">
<img alt="" border="0" width="1" height="1" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" >
</form>

Create success.php

//Get payment information from PayPal
$item_number = $_GET['item_number']; 
$txn_id = $_GET['tx'];
$payment_gross = $_GET['amt'];
$currency_code = $_GET['cc'];
$payment_status = $_GET['st'];

Create ipn.php
/*
 * Read POST data
 * reading posted data directly from $_POST causes serialization
 * issues with array data in POST.
 * Reading raw POST data from input stream instead.
 */       
$raw_post_data = file_get_contents('php://input');
$raw_post_array = explode('&', $raw_post_data);
$result = array();
foreach ($raw_post_array as $keyval) {
    $keyval = explode ('=', $keyval);
    if (count($keyval) == 2)
        $result[$keyval[0]] = urldecode($keyval[1]);
}
$req = 'cmd=_notify-validate';
$get_magic_quotes_exists = false;
if (function_exists('get_magic_quotes_gpc')) {
$get_magic_quotes_exists = true;
}
foreach ($result as $key => $value) {
    if ($get_magic_quotes_exists == true && get_magic_quotes_gpc() == 1) {
$value = urlencode(stripslashes($value));
} else {
$value = urlencode($value);
}
    $req .= "&$key=$value";
}

/*
 * Post IPN data back to PayPal to validate the IPN data is genuine
 * Without this step anyone can fake IPN data
 */
$paypalURL = "https://www.sandbox.paypal.com/cgi-bin/webscr";
$ch = curl_init($paypalURL);
if ($ch == FALSE) {
    return FALSE;
}
curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
curl_setopt($ch, CURLOPT_SSLVERSION, 6);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($ch, CURLOPT_FORBID_REUSE, 1);

// Set TCP timeout to 30 seconds
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Connection: Close', 'User-Agent: company-name'));
$res = curl_exec($ch);

/*
 * Inspect IPN validation result and act accordingly
 * Split response headers and payload, a better way for strcmp
 */
$tokens = explode("\r\n\r\n", trim($res));
$res = trim(end($tokens));
if (strcmp($res, "VERIFIED") == 0 || strcasecmp($res, "VERIFIED") == 0) {
    
// Payment data
$item_name = $_POST['item_name'];
$item_number = $_POST['item_number'];
$payment_status = $_POST['payment_status'];
$payment_amount = $_POST['mc_gross'];
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$payer_email = $_POST['payer_email'];
    
// check whether the payment_status is Completed
$isPaymentCompleted = false;
if($payment_status == "Completed") {
$isPaymentCompleted = true;
}


}