Prepare the SOAP message for sending to the server.

def prepare(self):
        """Prepare the SOAP message for sending to the server."""
        headers = self.prepare_headers(self.http_headers, self.soap_action)

        soap_header = self.prepare_soap_header(self.soap_header)
        soap_body = self.prepare_soap_body(
            self.method, self.parameters, self.namespace
        )
        data = self.prepare_soap_envelope(soap_header, soap_body)
        return (headers, data)