Add: Getting items by its ids

lib/tools/items.dart

@@ -37,15 +37,19 @@ Future<List<GymItem>> getItemsByIds(
     BuildContext context, List<String> ids) async {
   final token = context.read<GymLinkProvider>().token;
   if (token != '') {
+    if (ids.isEmpty) {
+      return [];
+    }
     final Uri url =
         Uri.http('gymlink.freemyip.com:8080', 'api/product/get-products');
     try {
       final response = await http.post(url,
           headers: {
             'Authorization': 'Bearer $token',
+            'Content-Type': 'application/json'
           },
-          body: jsonEncode(ids.toList()));
-      if (response.statusCode == 200) {
+          body: jsonEncode({"ids": ids}));
+      if (response.statusCode == 201) {
         final data =
             jsonDecode(utf8.decode(response.bodyBytes)) as List<dynamic>;
         final items = data.map((e) => GymItem.fromJson(e)).toList();