React-native: Axios not working on ios but working on android. Error: JSON Value '' of type NSNull cannot be converted to NSString

I ran the debugger and axios is failing in sending the request. The same thing works perfectly in Android. As soon as it sends the request through axios then these red screens pop up on the emulator:

This is the code that is giving the error:

 /*red screen here after request send*/return axios.get(config.backend_url + '/api/firebase-user/' + firebaseId)
          .then((userDataFetchResult) => {
            dispatch(setUserGeneralData(userDataFetchResult.data.data));
            dispatch(authOperationFinished());
            return userData;
          })
          .catch(err => {
            console.log(err);
            dispatch(authOperationFailed(err));

          });

My package.json:

"dependencies": {
    "axios": "^0.18.0",
    "lodash": "^4.17.5",
    "native-base": "^2.4.1",
    "react": "16.3.1",
    "react-native": "0.54.1",
    "react-native-app-intro-slider": "^0.2.4",
    "react-native-datepicker": "^1.7.1",
    "react-native-fbsdk": "^0.7.0",
    "react-native-firebase": "^4.0.0",
    "react-native-image-picker": "^0.26.7",
    "react-native-navigation": "^1.1.444",
    "react-native-twitter-signin": "^1.0.2",
    "react-native-vector-icons": "^4.6.0",
    "react-redux": "^5.0.6",
    "redux": "^3.7.2",
    "redux-thunk": "^2.2.0"
  }

My info.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN""http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>CFBundleURLTypes</key>
    <array>
        <dict>
            <key>CFBundleURLSchemes</key>
            <array>
                <string>fbXXXXXXX</string>
            </array>
        </dict>
    </array>
    <key>LSApplicationQueriesSchemes</key>
    <array>
        <string>fbapi</string>
        <string>fb-messenger-share-api</string>
        <string>fbauth2</string>
        <string>fbshareextension</string>
    </array>
    <key>NSCameraUsageDescription</key>
    <string>Camera Permissions</string>
    <key>NSPhotoLibraryUsageDescription</key>
    <string>Gallery Permissions</string>
    <key>UIAppFonts</key>
    <array>
        <string>Ionicons.ttf</string>
    </array>
    <key>CFBundleDevelopmentRegion</key>
    <string>en</string>
    <key>CFBundleDisplayName</key>
    <string>FFFF</string>
    <key>CFBundleExecutable</key>
    <string>$(EXECUTABLE_NAME)</string>
    <key>CFBundleIdentifier</key>
    <string>org.reactjs.native.example.$(PRODUCT_NAME:rfc1034identifier)</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>$(PRODUCT_NAME)</string>
    <key>CFBundlePackageType</key>
    <string>APPL</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleSignature</key>
    <string>????</string>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>LSRequiresIPhoneOS</key>
    <true/>
    <key>UILaunchStoryboardName</key>
    <string>LaunchScreen</string>
    <key>UIRequiredDeviceCapabilities</key>
    <array>
        <string>armv7</string>
    </array>
    <key>UISupportedInterfaceOrientations</key>
    <array>
        <string>UIInterfaceOrientationPortrait</string>
        <string>UIInterfaceOrientationLandscapeLeft</string>
        <string>UIInterfaceOrientationLandscapeRight</string>
    </array>
    <key>UIViewControllerBasedStatusBarAppearance</key>
    <false/>
    <key>NSLocationWhenInUseUsageDescription</key>
    <string></string>
    <key>NSAppTransportSecurity</key>
    <dict>
        <key>NSAllowsArbitraryLoads</key>
        <true/>
        <key>NSExceptionDomains</key>
        <dict>
            <key>localhost</key>
            <dict>
                <key>NSExceptionAllowsInsecureHTTPLoads</key>
                <true/>
            </dict>
        </dict>
    </dict>
    <key>FacebookAppID</key>
    <string>XXXXXX</string>
    <key>FacebookDisplayName</key>
    <string>FF</string>
</dict>
</plist>

My AppDelegate.m:

#import "AppDelegate.h"
#import <React/RCTBundleURLProvider.h>
#import <FBSDKCoreKit/FBSDKCoreKit.h>

// **********************************************
// *** DON'T MISS: THE NEXT LINE IS IMPORTANT ***
// **********************************************
#import <TwitterKit/TwitterKit.h>

// IMPORTANT: if you're getting an Xcode error that RCCManager.h isn't found, you've probably ran "npm install"
// with npm ver 2. You'll need to "npm install" with npm 3 (see https://github.com/wix/react-native-navigation/issues/1)

#import <Firebase.h>
#import "RCCManager.h"

#import <React/RCTRootView.h>

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [FIRApp configure];

  [[FBSDKApplicationDelegate sharedInstance] application:application
                           didFinishLaunchingWithOptions:launchOptions];


  NSURL *jsCodeLocation;
#ifdef DEBUG
  jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
#else
  jsCodeLocation = [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];
#endif

  self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
  self.window.backgroundColor = [UIColor whiteColor];
  [[RCCManager sharedInstance] initBridgeWithBundleURL:jsCodeLocation launchOptions:launchOptions];

  return YES;
}

- (BOOL)application:(UIApplication *)application
            openURL:(NSURL *)url
            options:(NSDictionary<NSString *,id> *)options {

  BOOL handled = [[FBSDKApplicationDelegate sharedInstance] application:application
                                                                openURL:url
                                                      sourceApplication:options[UIApplicationOpenURLOptionsSourceApplicationKey]
                                                             annotation:options[UIApplicationOpenURLOptionsAnnotationKey]
                  ];

  BOOL handledT = [[Twitter sharedInstance] application:application openURL:url options:options];
  // Add any custom logic here.
  return handled || handledT;
}


- (void)applicationDidBecomeActive:(UIApplication *)application {
  [FBSDKAppEvents activateApp];
}

@end

Any idea of what could be the problem? Thank you very much!

EDIT: Aparently the request data arrives but it throws the red screen anyway. The render method of the component that calls it runs several times as well before throwing the error. Im calling it on componentDidMount. The render method is

render() {

    let content = (
      <CausesList
        causes={this.props.causes}
        onItemSelected={this.itemSelectedHandler}
        onLoadMore={this.onLoadMoreHandler}
      />
    ); 


    let spinner = null;

    if (this.props.causesFetchLoading || this.state.checkingFirebaseAuth) {
      spinner = <ActivityIndicator />
    }

     return (
      <View>
           <SearchBar onSearch={this.onShearchHandler} />
           <CauseCategoriesList causeCategories={this.props.causeCategories} onCategoryPressed={this.onCategoryPressedHandler} /> 
          {content}
          {spinner}
      </View>
    );
  }
}

EDIT 2: It seems that is has nothing to do with networking. I've been following the program with the debugger and it fails when it renders the components. It must be doing some conversion that is accepted in android but not in ios....