private func subscribeToGeoTracks(args: Dictionary<String, Any>, flutterResult: @escaping FlutterResult) {
        do {
            let subscriptionKey = UUID().uuidString
            let userId = args["userId"] as! Int
            let subscription = NotifiedByLocationLambdaSubscription(userId: userId)
            let watcher = try self.client!.subscribe(subscription: subscription, resultHandler: ({ (result, transaction, error) in
                if error != nil {
                    self.channel.invokeMethod(subscriptionKey + "@" + AppSyncPlugin.SUBSCRIBE_TO_GEO_TRACKS_ERROR,
                                              arguments: error!.localizedDescription)
                } else {
                    if let _ = result!.data?.notifiedByLocationLambda {
                        let values = result!.data!.snapshot
                        do {
                            let jsonData = try JSONSerialization.data(withJSONObject: values, options: .prettyPrinted)
                            let convertedString = String(data: jsonData, encoding: String.Encoding.utf8)
                            self.channel.invokeMethod(subscriptionKey + "@" + AppSyncPlugin.SUBSCRIBE_TO_GEO_TRACKS_RESULT, arguments: convertedString)
                        } catch {
                            flutterResult(FlutterError(code: "APP_ERROR", message: error.localizedDescription, details: nil))
                        }
                    }
                }
            }))
            geoTracksSubscriptions[subscriptionKey] = watcher
            flutterResult(subscriptionKey)
        } catch {
            flutterResult(FlutterError(code: "QUERY_ERROR", message: error.localizedDescription, details: nil))
        }
    }