def METHOD_NAME(self, request: PipelineRequest) -> None:  # type: ignore # pylint: disable=arguments-differ
    """This is executed before sending the request to the next policy.
    :param request: The PipelineRequest object.
    :type request: ~azure.core.pipeline.PipelineRequest
    """
    with self._lock:
        sync_token_header = ",".join(str(x) for x in self._sync_tokens.values())
        if sync_token_header:
            request.http_request.headers.update({self._sync_token_header: sync_token_header})