How to get data from Future<dynamic> function Flutter

Question

I'm getting data with this function:

 Future<dynamic> getItem(String endpoint, List<String> pathParams) async {
   final uri = buildUri(endpoint, pathParams, {});
   final response = await http.get(uri, headers: {
     'Authorization': 'Bearer $_ACCESS_TOKEN',
     'Content-Type': 'application/json'
   });
   if (response.statusCode == _UNAUTHORIZED) {
     return _refresh(
         () => getItem(endpoint, pathParams), () => _redirectToLogin());
   }
   return response.body;
 }

When I try to use the data like this:

 List user = [];
 void getItem() async {
   List tmp = await ac.getItem("/v1/users/:0", [idProfile]);
   if (mounted) {
     setState(() {
       user = tmp;
     });
   }
 }

It sais me: it's not a subtype... I've tried with List, List, List, Map, Map<String, dynamic>, and nothing works. What type should I use?