Custom Parameters are always Null | Firebase Dynamic Links - flutter

Question

What I Want to Do
When the user taps the URL, it launches the app and pops up a page within the app based on the included custom parameters.
Problem
I succeeded in launching an Android or iOS app by tapping the URL, but the custom parameter is always null.
What I Did
The URL that users tap is as follows.
https://example.page.link/test/?link=https://test.example.com/?id=${id}&apn=com.example.app
id is custom parameter that I want to get when this URL is called.
I created link on Firebase Console like example.page.link/test.
In initState, call initDeepLinks function.
// openPage opens detail page with id
Future<void> initDeepLinks() async {
final PendingDynamicLinkData? initialLink =
await FirebaseDynamicLinks.instance.getInitialLink();
if (initialLink != null) {
final Uri deepLink = initialLink.link;
print("A: " + deepLink.queryParameters["id"]!);
openPage(deepLink.queryParameters["id"]!);
}
FirebaseDynamicLinks.instance.onLink.listen((dynamicLinkData) {
print("B: " + dynamicLinkData.link.queryParameters["id"]!);
openPage(dynamicLinkData.link.queryParameters["id"]!);
}).onError((error) {});
}
But those two print()s print only A: or B: .
I checked URL that contains ?id=$id and it is correct.
Tried other URL
When I change the URL to
https://example.page.link/?link=https://test.example.com/?id=${id}&apn=com.example.app
(removed `/test` path)
It works with custom parameters only on Android.
But do same on iOS, the browser shows https://test.example.com page and app doesn't appear.
What should I do to make custom parameters?