Cannot modify header information - When sending more than 2 emails with PHPMailer

I am trying to send different emails to users of the application, it turns out that if I send more than 2 it gives me the error:

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\project\app\PHPMailer\class.smtp.php:239) in C:\xampp\htdocs\project\app\actionAdmin\ insert-offer.php on line 37

The error refers to a header that I have, but what I don't understand is why with 2 it works correctly, it does the header for me, and if there are 3 the header doesn't do it for me anymore, the application does its job of sending the mails correctly, but it does not redirect me. I don't really know what to do anymore. Goodnight

  foreach( $email  as  $email ){

                 $mail->IsSMTP(); // enable SMTP
                 $mail->SMTPDebug = 1; // debugging: 1 = errors and messages, 2 = messages only
                 $mail->SMTPAuth = true; // authentication enabled
                 $mail->SMTPSecure = 'ssl'; // secure transfer enabled REQUIRED for Gmail
                 $mail->Host = "smtp.gmail.com";
                 $mail->Port = 465; // or 587
                 $mail->IsHTML(true);
                 $mail->Username = "[email protected]";
                 $mail->Password = "corominesempleo20";
                 $mail->SetFrom($email['email']);
                 $mail->Subject = $titulo;
                 $mail->Body = $cuerpo;
                 $mail->AddAddress($email['email']);

                    if(!$mail->Send()) {
                    echo "Mailer Error: " . $mail->ErrorInfo;
                    } else {
                    echo "Message has been sent";
                    }
            }    

            $carpeta = "../actionAdmin/files/";
            opendir($carpeta);
            $destino = $carpeta.$_FILES['imagen']['name'];
            copy($_FILES['imagen']['tmp_name'],$destino);

            $nombreImg = $_FILES['imagen']['name'];


    $administrador->agregarOferta($titulo,$empresa,$email,$sector,$localidad,$descripcion,$nombreImg,$destino);

    $administrador->getEmail('Oferta de Empleo nueva','Estos son los datos de la oferta');

    $_SESSION['insertado'] = 'insertado';
      header("Location: ../views/panel-admin.php");
              exit();
    }