code: public static void sendNackToPebble(final Context context, final int transactionId)
              throws IllegalArgumentException {
  
          if ((transactionId & ~0xff) != 0) {
              throw new IllegalArgumentException(String.format(
                      "transaction id must be between (0, 255); got '%d'", transactionId));
          }
  
          final Intent nackIntent = new Intent(INTENT_APP_NACK);
          nackIntent.putExtra(TRANSACTION_ID, transactionId);
          context.sendBroadcast(nackIntent);
      }
docs: Send a message to the connected watch that the previously sent PebbleDictionary was not received successfully. To
  avoid protocol timeouts on the watch, applications <em>must</em> ACK or NACK all received messages.
  
  @param context
  The context used to send the broadcast.
  @param transactionId
  The transaction id of the message in which the data was received. Valid transaction IDs are between (0,
  255).
  
  @throws IllegalArgumentException
  Thrown if an invalid transaction id is specified.