Fix

app.py

@@ -69,14 +69,13 @@ def listen():
     if request.method == 'POST':
         payload = request.json
         event = payload['entry'][0]['messaging']
-        res = "ok"
         for x in event:
             if is_user_message(x):
                 text = x['message']['text']
                 sender_id = x['sender']['id']
-                res = respond(sender_id, text)
+                respond(sender_id, text)
 
-        return res
+        return "ok"
 
 
 def send_message(recipient_id, text):