Uncaught Error: Call to undefined method Database::prepare()

<?php

class Database
{
  private $db_host        = 'localhost';
  private $db_name        = 'boom'; 
  private $db_port        = 3309;
  private $db_charset     = 'utf8';
  private $db_user        = 'root';
  private $db_password    = '';
  private $dsn;
  private $pdo;
  private $error;

  public function __construct()
  {
    $this->dsn = "mysql:host={$this->db_host};dbname={$this->db_name};port={$this->db_port};charset={$this->db_charset}";
    try {
      $this->pdo = new PDO($this->dsn, $this->db_user, $this->db_password);
      $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    } catch(PDOException $e) {
      echo $this->error = 'Erreur: ' . $e->getMessage();
    }
  }

  public function prepare(String $stmt, Array $fields = []):bool {
    $req = $this->pdo->prepare($stmt);
    $req->execute($fields);

    return $req;
  }

  public function is_already_in_use(String $field, String $value, String $table):bool
  {
    $req = $this->pdo->prepare("SELECT id FROM $table WHERE $field = ?");
    $req->execute([$value]);
    $count = $req->rowCount();
    $req->closeCursor();

    return $count;
  }

}

<?php
// Ouverture de la session 
session_start();

// URL
$host = $_SERVER['HTTP_HOST'];
$uri = $_SERVER['REQUEST_URI'];
$url = sprintf("%s%s%s", "http://", $host, $uri);

$http = explode('/', $url);
$http = $http[0] . '//' . $http[2] . '/' . $http[3];

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

// Envoi du courriel via PHPMailer
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$mail = new PHPMailer(true);

// Accès à la base de données
$bdd = new Database();

// Gestion des erreurs
$errors = new Errors();

// Traitement du formulaire soumis
if (isset($_POST['register'])) {
  // Tous les champs ont été remplis ?
    if (not_empty(['name', 'pseudo', 'email', 'password', 'password_confirm'])) {
        extract($_POST);
        if (mb_strlen($name) < 3) {
            $error = $errors->setError('Nom trop court (minimum 3 caractères)');
        }
        if (mb_strlen($pseudo) < 3) {
            $error = $errors->setError('Pseudonyme trop court (minimum 3 caractères)');
        }
        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            $error = $errors->setError('Adresse courriel invalide');
        }
        if (mb_strlen($password) < 6) {
            $error = $errors->setError('Mot de passe trop court (minimum 6 caractères)');
        } else {
            if ($password != $password_confirm) {
                $error = $errors->setError('Les deux mots de passe ne concordent pas');
            }
        }
        if ($bdd->is_already_in_use('pseudo', $pseudo, 'users')) {
            $error = $errors->setError('Pseudonyme déjà utilisé');
        }
        if ($bdd->is_already_in_use('email', $email, 'users')) {
            $error = $errors->setError('Adresse courriel déjà utilisée');
        }
        if ($errors->countError() == 0) {
            $token = sha1($pseudo . $email . $password);
            // Envoi d'un courriel d'activation
            try {
                //Server settings
                $mail->CharSet = 'UTF-8';
                //Recipients
                $mail->setFrom('contact@boom.com', 'Boom Social Network');
                $mail->addAddress($email, $name);
                //Content
                $mail->isHTML(true);
                $mail->Subject = 'Boom Social Network - ACTIVATION DE COMPTE';
                // Message HTML
                ob_start();
                require __DIR__ . '/templates/emails/activation.tmpl.php';
                $content = ob_get_clean();
                $mail->Body = $content;
                
                $saveIsOk = $bdd->prepare('INSERT INTO users(name, pseudo, email, password) 
                                      VALUE(:name, :pseudo, :email, :password)',
                                      [
                                          'name'     => $name,
                                          'pseudo'   => $pseudo,
                                          'email'    => $email,
                                          'password' => sha1($password)
                                      ]);
                if ($saveIsOk) {
                    // Informer l'utilisateur de vérifier sa boîte de réception
                    set_flash('Un courriel d\'activation de votre compte vous a été envoyé', 'success');
                    $mail->send();
                    // Redirection vers sa page de profil
                    redirect('index.php');
                }
            } catch (Exception $e) {
                echo 'Le courriel n\'a pas pu été envoyé.';
                echo 'Erreur: ' . $mail->ErrorInfo;
            }
        } else {
            save_input_data();
        }
    } else {
        $error = $errors->setError('Veuillez remplir tous les champs.');
        save_input_data();
    }
} else {
    clear_input_data();
}

// Titre
$title = 'Inscription';

// Page register.view.php
require __DIR__ . '/views/register.view.php';