Adding PHPMailer to an existing *.php

I have  3   <?php  ?>.  They are part of signup.php. In third one i did comment mail() ; function.

Because I want to use  an extra <?php  ?>, where i want to implement PHPMailer to send emails.  That one will then use $e variable (address where to send the email) from
 the third  <?php  ?>

But it is not functioning all together. Can you pleas  help me make  it work?
For info: If  I put next  part

$mail = new PHPMailer(true);                              
try {
............
}

Select allOpen in new window

from the fourth  <?php  ?> into comments, then the page loads.
And another info:  I can use  PHPMailer library as separate app. So, my PHPMailer settings are Ok.

<?php  
...
...
?>
<?php
// Ajax calls this NAME CHECK code to execute
if(isset($_POST["usernamecheck"])){
	include_once("xxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
	$username = preg_replace('#[^a-z0-9]#i', '', $_POST['usernamecheck']);
	$sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
    $query = mysqli_query($db_conx, $sql); 
    $uname_check = mysqli_num_rows($query);
    if (strlen($username) < 3 || strlen($username) > 16) {
	    echo '<strong style="color:#F00;">3 - 16 characters please</strong>';
	    exit();
    }
	if (is_numeric($username[0])) {
	    echo '<strong style="color:#F00;">Usernames must begin with a letter aha</strong>';
	    exit();
    }
    if ($uname_check < 1) {
	    echo '<strong style="color:#009900;">' . $username . ' is OK</strong>';
	    exit();
    } else {
	    echo '<strong style="color:#F00;">' . $username . ' is taken</strong>';
	    exit();
    }
}
?><?php
// Ajax calls this REGISTRATION code to execute
if(isset($_POST["u"])){
	// CONNECT TO THE DATABASE
	include_once("../php_includes/db_conx.php");
	// GATHER THE POSTED DATA INTO LOCAL VARIABLES
	$u = preg_replace('#[^a-z0-9]#i', '', $_POST['u']);
	$e = mysqli_real_escape_string($db_conx, $_POST['e']);
	$p = $_POST['p'];
	$g = preg_replace('#[^a-z]#', '', $_POST['g']);
	$c = preg_replace('#[^a-z ]#i', '', $_POST['c']);
	// GET USER IP ADDRESS
    $ip = preg_replace('#[^0-9.]#', '', getenv('REMOTE_ADDR'));
	// DUPLICATE DATA CHECKS FOR USERNAME AND EMAIL
	$sql = "SELECT id FROM users WHERE username='$u' LIMIT 1";
    $query = mysqli_query($db_conx, $sql); 
	$u_check = mysqli_num_rows($query);
	// -------------------------------------------
	$sql = "SELECT id FROM users WHERE email='$e' LIMIT 1";
    $query = mysqli_query($db_conx, $sql); 
	$e_check = mysqli_num_rows($query);
	// FORM DATA ERROR HANDLING
	if($u == "" || $e == "" || $p == "" || $g == "" || $c == ""){
		echo "The form submission is missing values ma kaj.";
        exit();
	} else if ($u_check > 0){ 
        echo "The username you entered is alreay taken";
        exit();
	} else if ($e_check > 0){ 
        echo "That email address is already in use in the system";
        exit();
	} else if (strlen($u) < 3 || strlen($u) > 16) {
        echo "Username must be between 3 and 16 characters";
        exit(); 
    } else if (is_numeric($u[0])) {
        echo 'Username cannot begin with a number';
        exit();
    } else {
	// END FORM DATA ERROR HANDLING
	    // Begin Insertion of data into the database
		// Hash the password and apply your own mysterious unique salt
		
		
		$p_hash = md5($p);
		// Add user info into the database table for the main site table
		$sql = "INSERT INTO users (username, email, password, gender, country, ip, signup, lastlogin, notescheck)       
		        VALUES('$u','$e','$p_hash','$g','$c','$ip',now(),now(),now())";
		$query = mysqli_query($db_conx, $sql); 
		$uid = mysqli_insert_id($db_conx);
		// Establish their row in the useroptions table
		$sql = "INSERT INTO useroptions (id, username, background) VALUES ('$uid','$u','original')";
		$query = mysqli_query($db_conx, $sql);
		// Create directory(folder) to hold each user's files(pics, MP3s, etc.)
		    if (!file_exists("../user/$u")) {
			mkdir("../user/$u", 0755);
		}
		  if (!file_exists("../user/$u/projectsList2")) {
			mkdir("../user/$u/projectsList2", 0755);
		}
		// Email the user their activation link
	/*$to = "$e";							 
		$from = "xxxxxxxxxxx";
		$subject = 'xxxxxxxxxxxxxxx';
		$message = 'xxxxxxxxxxx';
		$headers = "From: $from\n";
        $headers .= "MIME-Version: 1.0\n";
        $headers .= "Content-type: text/html; charset=iso-8859-1\n";
		mail($to, $subject, $message, $headers);
		echo "signup_success";*/
		exit();
	}
	exit();
}
?>	
<?php

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

require  '../vendor/autoload.php';

$mail = new PHPMailer(true);                              
try {
    //Server settings
    $mail->SMTPDebug = 2;                                
    $mail->isSMTP();                                      
    $mail->Host = 'xxxxxxxxxxxxx';                     
    $mail->SMTPAuth = true;                               
    $mail->Username = 'xxxxxxxxxx';              
    $mail->Password = 'xxxxxxxxxxxxxx';                          
    $mail->SMTPSecure = 'tls';                            
    $mail->Port = 587;                                    

    //Recipients
    $mail->setFrom('xxxxxxxxxxxxxx');
    $mail->addAddress('xxxxxxxxxxx);     
   // $mail->addAddress('xxxxxxxxxx');               

   // $mail->addCC('cc@example.com');
    //$mail->addBCC('bcc@example.com');
  //
  
    //Content
    $mail->isHTML(true);                                  
    $mail->Subject = 'xxxxxxxxxxxxxx';
    $mail->Body    = '';
	
    $mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

    $mail->send();
    
} 
?>

Select allOpen in new window