PHP - Php Form Keeps Sending Me Blank

I have a form with a gender control made up of two radio buttons.

If the user doesn't fill out this form, nothing gets submitted (i.e name='gender') in the $_POST array.

So how ae you supposed to verify that the form field was left blank, and use that information to say display an error message on the form?

I have phpmailer on a website and after clicking send, it goes to the forms action page and don't seem to redirect to the enquiry confirmation page, the forms action page is a blank white page which am guessing is correct as it's PHP coding but thought it should redirect. I don't get any errors showing what the issue is. I have the phpmailer uploaded onto the FTP server and has the class.phpmailer.php file inside the phpmailer folder. The client has their email going through office365. Below is the code I have

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<?php

ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');
error_reporting(E_ALL);

//index.php

$error = '';
$name = '';
$email = '';
$subject = '';
$message = '';

function clean_text($string)
{
$string = trim($string);
$string = stripslashes($string);
$string = htmlspecialchars($string);
return $string;
}

if(isset($_POST["submit"]))
{
if(empty($_POST["name"]))
{
$error .= '<p><label class="text-danger">Please Enter your Name</label></p>';
}
else
{
$name = clean_text($_POST["name"]);
if(!preg_match("/^[a-zA-Z ]*$/",$name))
{
$error .= '<p><label class="text-danger">Only letters and white space allowed</label></p>';
}
}
if(empty($_POST["email"]))
{
$error .= '<p><label class="text-danger">Please Enter your Email</label></p>';
}
else
{
$email = clean_text($_POST["email"]);
if(!filter_var($email, FILTER_VALIDATE_EMAIL))
{
$error .= '<p><label class="text-danger">Invalid email format</label></p>';
}
}
if(empty($_POST["subject"]))
{
$error .= '<p><label class="text-danger">Subject is required</label></p>';
}
else
{
$subject = clean_text($_POST["subject"]);
}
if(empty($_POST["message"]))
{
$error .= '<p><label class="text-danger">Message is required</label></p>';
}
else
{
$message = clean_text($_POST["message"]);
}
if($error == '')
{

require 'phpmailer/class.phpmailer.php';
$mail = new PHPMailer;
$mail->SMTPDebug  = 2;
$mail->IsSMTP();        //Sets Mailer to send message using SMTP
$mail->Host = 'smtp.office365.com';  //Sets the SMTP hosts
$mail->Port = '587';        //Sets the default SMTP server port
$mail->SMTPSecure = 'tls';       //Sets connection prefix. Options are "", "ssl" or "tls"
$mail->SMTPAuth = true;       //Sets SMTP authentication. Utilizes the Username and Password variables
$mail->Username = 'email@domain.co.uk';     //Sets SMTP username
$mail->Password = 'password';     //Sets SMTP password
$mail->From = $_POST["email"];     //Sets the From email address for the message
$mail->FromName = $_POST["name"];    //Sets the From name of the message
$mail->AddAddress('email@domain.co.uk', 'Name');//Adds a "To" address
$mail->AddCC($_POST["email"], $_POST["name"]); //Adds a "Cc" address
$mail->WordWrap = 50;       //Sets word wrapping on the body of the message to a given number of characters
$mail->IsHTML(true);       //Sets message type to HTML    
$mail->Subject = "New Website Enquiry";    //Sets the Subject of the message
$mail->Body = "Name: " . $_POST["name"] . "<br><br>" . "Email: " . $_POST["email"] . "<br><br>" . "Subject: " . $_POST["subject"] . "<br><br>" . "Message: " . "<br>" . $_POST["message"];    //An HTML or plain text message body
if (!$mail->Send())        //Send an Email. Return true on success or false on error
{
header('Location: https://www.domain.co.uk/enquiry-confirmation.php');
}
else
{
$error = '<label class="text-danger">There is an Error</label>';
}
$name = '';
$email = '';
$subject = '';
$message = '';
}
}
?>

<?php require_once('Connections/conexxion.php'); ?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") 
{
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  }

  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO movimiento (venta, compra, taller, regula_mas, regula_menos, id_lente, id_cil, id_esf) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)",
                       GetSQLValueString($_POST['venta'], "int"),
                       GetSQLValueString($_POST['compra'], "int"),
                       GetSQLValueString($_POST['taller'], "int"),
                       GetSQLValueString($_POST['regula_mas'], "int"),
                       GetSQLValueString($_POST['regula_menos'], "int"),
                       GetSQLValueString($_POST['id_lente'], "int"),
                       GetSQLValueString($_POST['id_cil'], "int"),
                       GetSQLValueString($_POST['id_esf'], "int"));

  mysql_select_db($database_conexxion, $conexxion);
  $Result1 = mysql_query($insertSQL, $conexxion) or die(mysql_error());
}

mysql_select_db($database_conexxion, $conexxion);
$query_lente = "select id_lente, lente from lentes";
$lente = mysql_query($query_lente, $conexxion) or die(mysql_error());
$row_lente = mysql_fetch_assoc($lente);
$totalRows_lente = mysql_num_rows($lente);

mysql_select_db($database_conexxion, $conexxion);
$query_esfera = "SELECT  * FROM esfera";
$esfera = mysql_query($query_esfera, $conexxion) or die(mysql_error());

mysql_select_db($database_conexxion, $conexxion);
$query_cilindro = "SELECT * FROM cilindro";
$cilindro = mysql_query($query_cilindro, $conexxion) or die(mysql_error());

$query_item = "select id_item from item
inner join rx on rx.id_rx = item.id_rx
inner join cilindro on cilindro.id_cil = rx.id_cil
inner join esfera on esfera.id_esf = rx.id_esf
where cilindro = ".$_POST['sel_cil']." and esfera = ".$_POST['sel_esf']." and id_lente =". $_POST['sel_lente'];
$idlente = mysql_query($query_lente, $conexxion) or die (mysql_error());


?>

<form action="<?php echo $editFormAction; ?>" method="post" name="form1" id="form1">
  <table align="center">
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Venta:</td>
      <td><input type="text" name="venta" value="" size="32" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Compra:</td>
      <td><input type="text" name="compra" value="" size="32" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Taller:</td>
      <td><input type="text" name="taller" value="" size="32" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Regula_mas:</td>
      <td><input type="text" name="regula_mas" value="" size="32" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Regula_menos:</td>
      <td><input type="text" name="regula_menos" value="" size="32" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">lente:</td>
      <td><?php echo "<select name='sel_lente'>";
while($row= mysql_fetch_array($lente)){?>
<option value=" <?php echo $row['id_lente'] ;?> " > <?php echo $row['lente']; ?> </option>
    <?php } ?> </select>
    <label for="id_lente"></label></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">cilindro:</td>
      <td><?php echo "<select name='sel_cil'>";
while($row= mysql_fetch_array($cilindro)){?>
<option value=" <?php echo $row['id_cil'] ;?> " > <?php echo $row['cilindro']; ?> </option>
    <?php } ?> </select>
    <label for="id_cil"></label></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">Esfera:</td>
      <td><?php echo "<select name='sel_esf'>";
while($row= mysql_fetch_array($esfera)){?>
<option value=" <?php echo $row['id_esf'] ;?> " > <?php echo $row['esfera']; ?> </option>
    <?php } ?> </select></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">id_lente</td>
      <td><label for="id_lente3"></label>
      <input type="text" name="id_lente" id="id_lente3" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">&nbsp;</td>
      <td><input type="submit" value="Insert record" /></td>
    </tr>
  </table>
  <input type="hidden" name="MM_insert" value="form1" />
</form>
<?php
mysql_free_result($esfera);

mysql_free_result($cilindro);

mysql_free_result($lente);
?>

$query_item = "select id_item from item
inner join rx on rx.id_rx = item.id_rx
inner join cilindro on cilindro.id_cil = rx.id_cil
inner join esfera on esfera.id_esf = rx.id_esf
where cilindro = ".$_POST['sel_cil']." and esfera = ".$_POST['sel_esf']." and id_lente =". $_POST['sel_lente'];
$idlente = mysql_query($query_lente, $conexxion) or die (mysql_error());