I am creating a booking system using php and paypal. Now testing with sandbox,

when I try to pay with the test buy account, the IPN is 'VERIFIED' but when try to pay using the credit card (test) the ipn return 'INVALID'

Why is that?

All the fields are received correctly to the IPN script page.

The payment is received correctly on my paypal sandbox account, when checking the payment.

Here is the code:

$req = 'cmd=_notify-validate';
foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req.= "&$key=$value";
$ipn_content.= "$key=$value";
}

// post back to PayPal system to validate
$header="";
$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
$fp = fsockopen('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);


$VERIFIED=FALSE;

if (!$fp) {
// HTTP ERROR
} else {

fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
// check the payment_status is Completed
// check that txn_id has not been previously processed
// check that receiver_email is your Primary PayPal email
// check that payment_amount/payment_currency are correct
// process payment
$VERIFIED=TRUE;
}else if (strcmp ($res, "INVALID") == 0) {
// log for manual investigation
}

}

}
fclose ($fp);

echo $VERIFIED;

if($VERIFIED!=TRUE){
exit;
}

//continue.......