[Bug]: unable to appendUserAgent

I am unable to append or override the userAgent in my app, both android & ios.

/// <reference types="@capacitor/push-notifications" />
/// <reference types="@capacitor/splash-screen" />

import { CapacitorConfig } from '@capacitor/cli';

const config: CapacitorConfig = {
    appId: 'io.x.y',
    appName: 'XyApp',
    webDir: 'dist',
    plugins: {
        SplashScreen: {
            launchShowDuration: 5000,
            launchAutoHide: true,
            backgroundColor: '#ffffffff',
            androidSplashResourceName: 'splash',
            androidScaleType: 'CENTER_CROP',
            showSpinner: true,
            androidSpinnerStyle: 'large',
            iosSpinnerStyle: 'small',
            spinnerColor: '#999999',
            splashFullScreen: true,
            splashImmersive: false,
            layoutName: 'launch_screen',
            useDialog: false
        }
    },
    android: {
        appendUserAgent: 'XyApp'
    },
    ios: {
        appendUserAgent: 'XyApp'
    }
};

export default config;

whats wrong with this config?