Paypal Randomly Sometimes charging twice to my customers

[nasirzia]

Hi, I am using paypal website payment pro on my website, the payment code I use was the one I copied from paypal's official website.

Some of my users are being charged twice, however in CRM there is only one entry (which obviously means our code executes once only). I can't figure out, why randomly some of my visitors are being charged twice..

I am attaching the following source code to let you guys have an idea about the code..

    
        $f_name = $_POST['FIRSTNAME'];
        $l_name = $_POST['LASTNAME'];
        $street = $_POST['STREET'];
        $city = $_POST['CITY'];
        $state = $_POST['STATE'];
        $ZIP = $_POST['ZIP'];
        $title = $_POST['title'];
        $email = $_POST['email'];
        $perm = $_POST['perm'];
        $gift_aid = $_POST['gift_aid'];
        if($gift_aid == '1'){
            $gift_aid = 'true';
        }else{
            $gift_aid = 'false';
        }
        if($street == ''){
            $street = 'N/A';
        }
        if($city == ''){
            $city = 'N/A';
        }
        if($ZIP == ''){
            $ZIP = '0000';
        }
        $fulladdress = $_POST['fulladdress'];
        $data = 'VERSION=56.0&';
        $data .= 'SIGNATURE=AFK.XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
        $data .= '&';
        $data .= 'USER=XXXXXXXmyemailaddressXXXXXX';
        $data .= '&';
        $data .= 'PWD=XXXXXXXXXX';
        $data .= '&';
        $data .= 'METHOD=DoDirectPayment';
        $data .= '&';
        $data .= 'PAYMENTACTION=Sale';
        $data .= '&';
        $data .= 'IPADDRESS='.$_IP;
        $data .= '&';
        $data .= 'AMT='.$AMT;
        $data .= '&';
        $data .= 'CURRENCYCODE=GBP';
        $data .= '&';
        $data .= 'ACCT='.$ACCT;
        $data .= '&';
        $data .= 'EXPDATE='.$exp_year;
        $data .= '&';
        $data .= 'CVV2='.$CVV2;
        $data .= '&';
        $data .= 'FIRSTNAME='.$f_name;
        $data .= '&';
        $data .= 'LASTNAME='.$l_name;
        $data .= '&';
        $data .= 'STREET='.$street;
        $data .= '&';
        $data .= 'CITY='.$city;
        $data .= '&';
        $data .= 'STATE='.$state;
        $data .= '&';
        $data .= 'ZIP='.$ZIP;
        $data .= '&';
        $data .= 'COUNTRYCODE=US';
        
        
        
        $ch = curl_init();
        
        curl_setopt($ch, CURLOPT_URL, 'https://api-3t.paypal.com/nvp');
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
        
        $headers = array();
        $headers[] = 'Content-Type: application/x-www-form-urlencoded';
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
        
        $result = curl_exec($ch);
        if (curl_errno($ch)) {
            echo 'Error:' . curl_error($ch);
        }
        curl_close($ch);