Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'String?

I have a field in Firebase that contains values and each value is an id for a user document here

I fetched all the values from the array and stored them inside a variable as shown in the code below:

  List<dynamic> ids = [];
  Map<String, dynamic>? map;
  late  DocumentReference<Map<String, dynamic>> doc = databaseService.db.collection(userCollection).doc(auth.chatUser.uid);

Then I tried to insert all the values I got into a loop in order to fetch each member's data using the id's I got as shown :

  getIdsWithData() async {
var res = await doc.get();
setState(() {
  ids.clear();
  ids.add(res.data()!["requests"]);
});
for (var element in ids) {
  var data = await databaseService.db.collection(userCollection).doc(element).get();
  map = data.data();
}
print(map);}

But when executing the code, I get the error:

Unhandled Exception: type 'List' is not a subtype of type 'String?

I tried to solve by putting (.first) after (ids) and the problem was already solved as shown :

 for (var element in ids.first) {
  var data = await databaseService.db.collection(userCollection).doc(element).get();
  map = data.data();
}

but I face another problem, which is that I want to store these values from the loop to a variable that I use to display the member data in ListTile (listview.builder) as shown :

  Widget listView() {
return ListView.separated(
    itemCount: map!.length,
    separatorBuilder: (BuildContext context, int index) => const Divider(),
    itemBuilder: (BuildContext context, int index) {
      return CustomListTile(
          title: map![index]["name"],
          subtitle: map![index]["id"],
          image: map![index]["image"],
      );
    },
);}

Thanks for help