ödeme bildiri formu arıyorum

<? 
   
  $isim= $_POST['isim']; 
  $email= $_POST['email']; 
  $mesaj= $_POST['mesaj']; 
   
  if( $contact_name == true ) 
  { 
  $sender = $contact_email; 
   
  //your e-mail here :) 
  $receiver = "mailadresin@mailadresin.com"; 
   
  $client_ip = $_SERVER['REMOTE_ADDR']; 
  $email_body = "Ad Soyad: $isim\n\nEmail: $email\n\nMesaj:\n\n$mesaj\n\nIP: $client_ip \n\n"; //enter your site 
  $extra = "From: $sender\r\n" . "Reply-To: $sender \r\n" . "X-Mailer: PHP/" . phpversion(); 
   
  if( mail( $receiver, "Iletisim Formu - $contact_subject", $email_body, $extra ) )  
  { 
   echo ('<script language="javascript" type="text/javascript"> 
  alert("Mesajınız Başarıyla Gönderildi"); 
  </script>'); 
  } 
  else 
  { 
   header("location:gonderilemedi.php"); 
  } 
  } 
  ?> 
  <meta http-equiv="refresh" content="0; url=index.php">