diff --git a/apps/group_stat_api.py b/apps/group_stat_api.py
index 4a803fc..8d63c13 100644
--- a/apps/group_stat_api.py
+++ b/apps/group_stat_api.py
@@ -41,33 +41,47 @@ def top_users():
 def chat_activity():
     from_date = request.args.get("from_date")
     to_date = request.args.get("to_date")
+    
+    if not from_date or not to_date:
+        return jsonify({
+            "err": "from_date/to_date empty"
+        }),422
 
     date_format = request.args.get("date_format")
     group_by = request.args.get("group_by")
-
-    if not date_format:
-        date_format = "%Y-%m-%d"
-
-    if not group_by:
-        group_by = "day"
-
+    
+    group_by = group_by if group_by else "day"
+    date_format = date_format if date_format else "%Y-%m-%d"
+     
     dates = []
     counts = []
-
-    if from_date and to_date:
+    
+    try:
         from_date = datetime.strptime(from_date, date_format)
-        to_date = datetime.strptime(to_date, date_format)
-        
-        query = (Message
-            .select(fn.date_trunc(group_by, Message.timestamp).alias('range'), fn.count(Message.id).alias('count'))
-            .where((Message.timestamp >= from_date) & (Message.timestamp <= to_date))
-            .group_by(fn.date_trunc(group_by, Message.timestamp))
-            .order_by(SQL("range"))
-        )
+        to_date   = datetime.strptime(to_date, date_format)
+    except ValueError:
+        return jsonify({
+            "from_date": from_date,
+            "to_date": to_date,
+            "date_format": date_format,
+            "err":"can't format datatime obj"
+        }),422
+    
+    if not group_by in ["day","week","month","year"]:
+        return jsonify({
+            "err":"invalid group_by"
+        }),422
 
-        for group in query:
-            dates.append(group.range.strftime("%Y-%m-%d"))
-            counts.append(group.count)
+    query = (Message
+        .select(fn.date_trunc(group_by, Message.timestamp).alias('range'), fn.count(Message.id).alias('count'))
+        .where((Message.timestamp >= from_date) & (Message.timestamp <= to_date))
+        .group_by(fn.date_trunc(group_by, Message.timestamp))
+        .order_by(SQL("range"))
+    )
+
+    for group in query:
+        dates.append(group.range.strftime(date_format))
+        counts.append(group.count)
 
     return jsonify({
         "date": dates,