dkim.verify(email_message) TypeError: expected string or bytes-like object

def email():


    msg = MIMEMultipart()
    msg['Subject'] = 'test'
    msg['From'] = 'XXX'
    msg['To'] = 'XXX'
    msg.preamble = 'preamble'

    body = MIMEText("This is the body of the message")
    msg.attach(body)

    with open("test.csv") as fp:
        record = MIMEText(fp.read())
        record['Content-Disposition'] = 'attachment; filename="test.csv"'
        msg.attach(record)

    server = smtplib.SMTP('smtp.gmail.com', 587)
    server.ehlo()
    server.starttls()
    server.login("XXX", "XXX")
    server.sendmail("XXX", "XXX", msg.as_string())
    server.quit()