Error message when trying to send invoice

gistfile1.txt

Traceback (most recent call last):
  File "/opt/google_appengine/google/appengine/runtime/wsgi.py", line 267, in Handle
    result = handler(dict(self._environ), self._StartResponse)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1994, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1985, in wsgi_app
    response = self.handle_exception(e)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1540, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/chaim/repos/coligu/coligu-web/lib/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/chaim/repos/coligu/coligu-web/lib/flask_login.py", line 792, in decorated_view
    return func(*args, **kwargs)
  File "/home/chaim/repos/coligu/coligu-web/invoice.py", line 212, in send_invoice
    send_invoice_by_mail(invoice)
  File "/home/chaim/repos/coligu/coligu-web/invoice.py", line 291, in send_invoice_by_mail
    attachments=attachments
  File "/home/chaim/repos/coligu/coligu-web/mailer.py", line 12, in send_mail
    send_mail_to_recipient(attachments, from_email, from_name, recipient_email, html, reply_to, subject)
  File "/home/chaim/repos/coligu/coligu-web/mailer.py", line 30, in send_mail_to_recipient
    sg.client.mail.send.post(request_body=mail.get())
  File "/home/chaim/repos/coligu/coligu-web/lib/python_http_client/client.py", line 204, in http_request
    return Response(self._make_request(opener, request))
  File "/home/chaim/repos/coligu/coligu-web/lib/python_http_client/client.py", line 138, in _make_request
    return opener.open(request)
  File "/usr/lib/python2.7/urllib2.py", line 435, in open
    response = meth(req, response)
  File "/usr/lib/python2.7/urllib2.py", line 548, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.7/urllib2.py", line 473, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.7/urllib2.py", line 407, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 556, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
HTTPError: HTTP Error 400: Bad Request