PHP - Using Mysql Queries In Phpmailer To Send Mass Email To Certain Users

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 = '';
}
}
?>

Hello.
I have a form for users to make reservations and they have to pay for that.

I activate the Payment Gateway Platform (by Redsys in Spain), and it works fine asking you for card number and it goes through correctly and says PAYMENT OK, but the notification.PHP FILE does not work.

Could my server (SSL) configuration be the problem? or is it the CODE?

Any help about this, please, would be highly appreciated.

Thank you.

Part of the Nofication.php code is:

__________________________________________________________________________________

<?php
  @ini_set("display_errors","1");
  @ini_set("display_startup_errors","1");

  $handle = fopen("_redsys.log", "a");

  require_once("include/dbcommon.php");
  require_once("redsysHMAC256_API_PHP_4.0.2/apiRedsys.php"); 

  $miObj = new RedsysAPI; 

  $version = postvalue("Ds_SignatureVersion"); 
  $params = postvalue("Ds_MerchantParameters"); 
  $signatureRecibida = postvalue("Ds_Signature");

//  $version = "HMAC_SHA256_V1"; 
//  $params = "eyJEc19BbW91bnQiOiIyMDAiLCJEc19DdXJyZW5jeSI6Ijk3OCIsIkRzX09yZGVyIjoiMjAwNjE4MDkyNDMzIiwiRHNfTWVyY2hhbnRDb2RlIjoiOTk5MDA4ODgxIiwiRHNfVGVybWluYWwiOiIxIiwiRHNfUmVzcG9uc2UiOiI5OTk4IiwiRHNfQXV0aG9yaXNhdGlvbkNvZGUiOiIiLCJEc19UcmFuc2FjdGlvblR5cGUiOiIwIiwiRHNfU2VjdXJlUGF5bWVudCI6IjAiLCJEc19MYW5ndWFnZSI6IjEiLCJEc19NZXJjaGFudERhdGEiOiIifQ=="; 
//  $signatureRecibida = "Aa6GG9IfCYlRrj-yF5VxXg_qmhJ3R-fmfXxGvB8w2Sk="; 
  
  $txt = "version=".$version."\nparams=".$params."\nsignatureRecibida=".$signatureRecibida."\n";
  fwrite($handle,"\n\n\n".date("Y-m-d h:i:s")."\n");
  fwrite($handle,$txt);

  $decodec = $miObj->decodeMerchantParameters($params); 
  $codigoRespuesta = $miObj->getParameter("Ds_Response"); 

  $claveModuloAdmin = 'sq7HjrUOBfKmC576ILgskD5srU870gJ7'; 
  $signatureCalculada = $miObj->createMerchantSignatureNotif($claveModuloAdmin, $params); 
  $res = my_json_decode($decodec);
  fwrite($handle,$decodec."\n");
  

  if ($signatureCalculada === $signatureRecibida && $res["Ds_AuthorisationCode"]!="++++++" && !isset($res["Ds_ErrorCode"]) { 
  
    fwrite($handle,"Ds_Order = ".$res["Ds_Order"]."\n");
    DB::Query("update reservas set status=1 where Ds_Order='".$res["Ds_Order"]."'");
    $rs2 = DB::Query("select * from reservas where Ds_Order='".$res["Ds_Order"]."'");
    $values = $rs2->fetchAssoc();
    $email=$values['Email'];
    $msg="";
    $msg.= "El seu codi de reserva és: ". dechex(999999999-$values['Id_Reserva'])."<br>";
    $msg.= "Código sin cifrar: ". 999999999-$values['Id_Reserva']."<br>";
    $msg.= "Reserva descifrada ". (((hexdec(dechex(999999999-$values['Id_Reserva'])))-999999999)*-1)."<br>";
    $msg.= "La data de la seva reserva es : ".$values['Dia']."-".$values['Mes']."-".$values['Año']."<br>";

    $sql = "SELECT Espacio FROM Espacios WHERE Id_Espacio=" . $values["Id_Espacio"];
    $rs = CustomQuery($sql);
    $data = db_fetch_array($rs);
    //$result["txt"] = "Ãrea: " . $data["c"];
    //$msg.= "QR : " .$values['QR']."\r\n";         //json_decode($image, true);
    //<img src="http://www.htmldog.com/badge1.gif">          https://chart.googleapis.com/chart?cht=qr&chs=150x150&chl=12345678
    //$image2= '<img src="data:image/jpeg;base64,'.$values['QR'].'>';
    $msg.= '<img src="https://chart.googleapis.com/chart?cht=qr&chs=150x150&chl=http%3A%2F%2Fwww.sungest.net/reservas_list.php?qs='.dechex(999999999-$values['Id_Reserva']).'&f=all%2F&choe=UTF-8">';
    //echo '<img src="https://chart.googleapis.com/chart?cht=qr&chs=150x150&chl=http%3A%2F%2Fwww.sungest.net/reservas_list.php?qs='.dechex(999999999-$values['Id_Reserva']).'&f=all%2F&choe=UTF-8">';

    //    echo '<img src="data:image/jpeg;base64,'.$imageData.'">';
    //echo '<img src="data:image/jpeg;base64,'.$imageData.'">';
    //echo '<img src="data:image/jpeg;base64,'.$imageData.'">';
    $msg.= "<font size=4 color='Navy'><b>La seva reserva és per anar a : </b></font>". "<font size=5 color='Olive'><b>" .$data["Espacio"] . "</b></font><br>";
    $msg.= "<font size=4 color='Olive'><b>La seva àrea assignada és: </b></font>".$values['Id_Area']."<br>";

    $subject="La seva reserva per la platja";
    $ret=runner_mail(array('to' => $email, 'subject' => $subject, 'htmlbody' => $msg));
        echo "ok";
  } 
  else
      DB::Exec("delete from reservas where Ds_Order='".$res["Ds_Order"]."'");
fclose($handle);
?>

_______________________________________________________________________________________________

So I am trying to use PHP mailer on my site however it doesn't post to the email

Here is the code:

Top:

   <?php 

    use PHPMailer\PHPMailer\PHPMailer;
    use PHPMailer\PHPMailer\Exception;

    require 'vendor/phpmailer/phpmailer/src/Exception.php';
    require 'vendor/phpmailer/phpmailer/src/PHPMailer.php';
    require 'vendor/phpmailer/phpmailer/src/SMTP.php';
   ?>

Where it sends:

            require 'vendor/autoload.php';

            //Instantiation and passing `true` enables exceptions
            $mail = new PHPMailer(true);
            
            try {
                //Server settings
                $mail->SMTPDebug = SMTP::DEBUG_SERVER;                      //Enable verbose debug output
                $mail->isSMTP();                                            //Send using SMTP
                $mail->Host       = 'smtp.office365.com';                     //Set the SMTP server to send through
                $mail->SMTPAuth   = true;                                   //Enable SMTP authentication
                $mail->Username   = 'maileremail';                     //SMTP username
                $mail->Password   = 'mailerpassword';                               //SMTP password
                $mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;         //Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` encouraged
                $mail->Port       = 587;                                    //TCP port to connect to, use 465 for `PHPMailer::ENCRYPTION_SMTPS` above
            
                //Recipients
                $mail->setFrom('maileremail', 'Mailer');
                $mail->addAddress(myemail', 'Joe User');     //Add a recipient
            
                //Content
                $mail->isHTML(true);                                  //Set email format to HTML
                $mail->Subject = 'Here is the subject';
                $mail->Body    = 'This is the HTML message body <b>in bold!</b>';
                $mail->AltBody = 'This is the body in plain text for non-HTML mail clients';
            
                $mail->send();
                echo 'Message has been sent';
            } catch (Exception $e) {
                echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
            }
                  ?>

I have tried everything but it still won't post.