API returns JSON array not json object so that is List not Map.
i.e. User json is first element of Json Array.
So to get first element use first index. Inside fetch Info update
return Users.fromJson(jsonresponse[0]);

API returns JSON array, not JSON object so that is List, not Map.
i.e. if your model class name is User, User JSON is the first element of JSON Array.
So to get the first element use the first index. Inside fetch Info update
return Users.fromJson(jsonresponse[0]);