NERelay save to preferences error

I am developing an App based on Network Extension that lets all network requests on device access the Internet through a private Relay.

I created an empty iOS App and only the entitlements file and ViewController.swift(Main.storyboard) file have been modified. The code was copied from the official video https://developer.apple.com/videos/play/wwdc2023/10002/

But, running the App on iPhone, the saveToPreferences API reported Error Domain=NERelayErrorDomain Code=3 "(null)" and the App doesn't look like it's changed at all (it doesn't jump to the Settings - VPN&Relay). Does anyone know why？Any reply would be greatly appreciated.

• The contents of the entitlements file:

<?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>com.apple.developer.networking.networkextension</key>
	<array>
		<string>relay</string>
	</array>
</dict>
</plist>

• ViewController.swift:

import UIKit
import NetworkExtension

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    @IBAction func tap(_ sender: Any) {

        let newRelay = NERelay()
        let relayURL = URL(string: "https://relay.example.com:443/")
        newRelay.http3RelayURL = relayURL
        newRelay.http2RelayURL = relayURL

        newRelay.additionalHTTPHeaderFields = ["Authorization" : "PrivateToken=123"]

        let manager = NERelayManager.shared()
        manager.relays = [newRelay]
        manager.matchDomains = ["internal.example.com"]

        manager.isEnabled = false
        manager.saveToPreferences { err in
            print(err)
        }
        
    }
    
}