PHPMailer "Could not instantiate mail function." Using Mailtrap

I am trying to use Mailtrap to use PHPMailer, but I am getting an error, and am having trouble finding a solution. Most people suggest fixing this problem by using a SMTP server, but as you can see, I already am.

<?php

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

require 'vendor/autoload.php';

$mail = new PHPMailer(true);

try {
    $phpmailer = new PHPMailer();
    $phpmailer->isSMTP();
    $phpmailer->Host = 'smtp.mailtrap.io';
    $phpmailer->SMTPAuth = true;
    $phpmailer->Port = 2525;
    $phpmailer->Username = 'myusername';
    $phpmailer->Password = 'mypassword';
    $mail->SMTPDebug = 2;


    //Recipients
    $mail->setFrom('myemail', 'Mailer');
    $mail->addAddress('myemail', 'Joe User');     

    //Content
    $mail->isHTML(true);                                  
    $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}";
}