As I passing property from React Native to native iOS you need to check for native iOS to React Native property passing.

Here is my code

In iOS
**Appdelegate.h**

#import <UIKit/UIKit.h>
#import "React/RCTBridgeModule.h"

@import Firebase;
@interface AppDelegate : UIResponder <UIApplicationDelegate, RCTBridgeModule>

@property (strong, nonatomic) UIWindow *window;


@end

**Appdelegate.m**

#import "RCTBundleURLProvider.h"
#import <React/RCTLog.h>

@implementation AppDelegate

RCT_EXPORT_MODULE();
RCT_EXPORT_METHOD(addEvent:(NSString *)propertyName)
{
    //Here you get your property value
    var property = propertyName;
    RCTLogInfo(@"Pretending to create an event %@ at %@", areaId);
}

In React Native

MyComponent.js

import { NativeModules } from 'react-native';

var AppDelegate = NativeModules.AppDelegate;
AppDelegate.addEvent(value);