Trouble sending mail asynchronously

send_mail.py

@main.route("/mail/<int:_id>/<int:number>")
@login_required
def mailSession(_id, number):



    from flask_mail import Message
    from decorators import async
    from app import mail, create_app
    


    @async
    def send_async_email(app, msg):
        with app.app_context():
            mail.send(msg)

    def send_email(subject, sender, recipients, text_body, html_body):
        msg = Message(subject,
                     sender=sender,
                     recipients=recipients

        )
        msg.body = text_body
        msg.html = html_body
        send_async_email(create_app("default"), msg)

    


    stp_id = user.get_id()
    therapist = users_db.find_one({"stp_id": stp_id})
    patient = therapist["patients"][str(_id)]
    sessions = patient["sessions"]
    session = sessions[str(number)]

    mail_body = render_template(
        'sessionEmail.txt',
        user=user,
        number=number,
        patient=patient,
        session=session
    )
    mail_html = render_template(
        'sessionEmail.html',
        user=user,
        number=number,
        patient=patient,
        session=session
    )

    

    send_email(
        "Sesión de Flores de Bach",
        sender=therapist["name"],
        recipients=[patient["email"]],
        text_body=mail_body,
        html_body=mail_html

    )

    return redirect(url_for('main.showSession', _id=_id, number=number))