diff --git a/apps/njau_bot/src/http_handler/api_handler.erl b/apps/njau_bot/src/http_handler/api_handler.erl
index ca8f95a..37efc47 100644
--- a/apps/njau_bot/src/http_handler/api_handler.erl
+++ b/apps/njau_bot/src/http_handler/api_handler.erl
@@ -30,6 +30,7 @@ init(Req0, Opts) ->
             }, Resp, Req1),
             {ok, Req2, Opts};
         false ->
+            lager:debug("[api_handler] invalid sign: ~p", [Sign]),
             Req2 = cowboy_req:reply(500, #{
                 <<"Content-Type">> => <<"text/html;charset=utf-8">>
             }, <<"Internal Server Error">>, Req1),
@@ -39,7 +40,7 @@ init(Req0, Opts) ->
 handle_request("POST", "/api/device_info", _, Params) ->
     njau_bot_logger:write(jiffy:encode(Params, [force_utf8])),
 
-    {ok, 200, json_data(<<"hello world">>)};
+    {ok, 200, json_data(<<"ok">>)};
 
 handle_request(_, Path, _, _) ->
     Path1 = list_to_binary(Path),