code: def send(self, send_email=True):
          
          url = str(self.api.base_url + '{code}/status/').format(code=self.code)  # six.u messes this up
          payload = {
              'mark_as_sent': True,
              'send_email': send_email,
          }
          stat = self.api.connection.make_put(url, payload)
docs: Marks the invoice as sent in Holvi
  
          If send_email is False then the invoice is *not* automatically emailed to the recipient
          and your must take care of sending the invoice yourself.