code: func handleNotifyReceived(wsc *wsClient, icmd interface{}) (interface{}, error) {
  	cmd, ok := icmd.(*btcjson.NotifyReceivedCmd)
  	if !ok {
  		return nil, btcjson.ErrRPCInternal
  	}
  
  	// Decode addresses to validate input, but the strings slice is used
  	// directly if these are all ok.
  	err := checkAddressValidity(cmd.Addresses, wsc.server.cfg.ChainParams)
  	if err != nil {
  		return nil, err
  	}
  
  	wsc.server.ntfnMgr.RegisterTxOutAddressRequests(wsc, cmd.Addresses)
  	return nil, nil
  }
docs: // handleNotifyReceived implements the notifyreceived command extension for
  // websocket connections.