code: @Override
    public Task<FcmSendMessageResult> sendMessageToUsers(
        final Collection<String> userIds,
        final FcmSendMessageRequest request
    ) {
      return dispatcher.dispatchTask(new Callable<FcmSendMessageResult>() {
        @Override
        public FcmSendMessageResult call() {
          return proxy.sendMessageToUsers(userIds, request);
        }
      });
    }
docs: Sends an FCM message to the given set of Stitch users with the given request payload.
  
  @param userIds the Stitch users to send a message to.
  @param request the details of the message.
  @return A {@link Task} that contains the result of sending the message.