diff --git a/apps/emqx_modules/src/emqx_delayed_api.erl b/apps/emqx_modules/src/emqx_delayed_api.erl
index 8137d9e63..9199d7b2c 100644
--- a/apps/emqx_modules/src/emqx_delayed_api.erl
+++ b/apps/emqx_modules/src/emqx_delayed_api.erl
@@ -44,6 +44,7 @@
 
 -define(MESSAGE_ID_NOT_FOUND, 'MESSAGE_ID_NOT_FOUND').
 -define(MESSAGE_ID_SCHEMA_ERROR, 'MESSAGE_ID_SCHEMA_ERROR').
+-define(MAX_PAYLOAD_SIZE, 1048576). %% 1MB = 1024 x 1024
 
 api_spec() ->
     emqx_dashboard_swagger:spec(?MODULE).
@@ -157,11 +158,11 @@ delayed_message(get, #{bindings := #{msgid := Id}}) ->
     case emqx_delayed:get_delayed_message(Id) of
         {ok, Message} ->
             Payload = maps:get(payload, Message),
-            case size(Payload) > ?MAX_PAYLOAD_LENGTH of
+            case erlang:byte_size(Payload) > ?MAX_PAYLOAD_SIZE of
                 true ->
-                    {200, Message#{payload => ?PAYLOAD_TOO_LARGE}};
+                    {200, Message};
                 _ ->
-                    {200, Message#{payload => Payload}}
+                    {200, Message#{payload => base64:encode(Payload)}}
             end;
         {error, id_schema_error} ->
             {400, generate_http_code_map(id_schema_error, Id)};
diff --git a/apps/emqx_retainer/src/emqx_retainer_api.erl b/apps/emqx_retainer/src/emqx_retainer_api.erl
index 26d341b53..5424629d9 100644
--- a/apps/emqx_retainer/src/emqx_retainer_api.erl
+++ b/apps/emqx_retainer/src/emqx_retainer_api.erl
@@ -28,13 +28,14 @@
 
 -import(emqx_mgmt_api_configs, [gen_schema/1]).
 -import(emqx_mgmt_util, [ object_array_schema/2
+                        , object_schema/2
                         , schema/1
                         , schema/2
                         , error_schema/2
                         , page_params/0
                         , properties/1]).
 
--define(MAX_BASE64_PAYLOAD_SIZE, 1048576). %% 1MB = 1024 x 1024
+-define(MAX_PAYLOAD_SIZE, 1048576). %% 1MB = 1024 x 1024
 
 api_spec() ->
     {[lookup_retained_api(), with_topic_api(), config_api()], []}.
@@ -64,7 +65,7 @@ parameters() ->
 lookup_retained_api() ->
     Metadata = #{
         get => #{
-            description => <<"lookup matching messages">>,
+            description => <<"List retained messages">>,
             parameters => page_params(),
             responses => #{
                 <<"200">> => object_array_schema(
@@ -80,9 +81,10 @@ with_topic_api() ->
     MetaData = #{
         get => #{
             description => <<"lookup matching messages">>,
-            parameters => parameters() ++ page_params(),
+            parameters => parameters(),
             responses => #{
-                <<"200">> => object_array_schema(message_props(), <<"List retained messages">>),
+                <<"200">> => object_schema(message_props(), <<"List retained messages">>),
+                <<"404">> => error_schema(<<"Reatined Not Exists">>, ['NOT_FOUND']),
                 <<"405">> => schema(<<"NotAllowed">>)
             }
         },
@@ -139,35 +141,27 @@ config(put, #{body := Body}) ->
 %%------------------------------------------------------------------------------
 %% Interval Funcs
 %%------------------------------------------------------------------------------
-lookup_retained(get, Params) ->
-    lookup(undefined, Params, fun format_message/1).
+lookup_retained(get, #{query_string := Qs}) ->
+    Page = maps:get(page, Qs, 1),
+    Limit = maps:get(page, Qs, emqx_mgmt:max_row_limit()),
+    {ok, Msgs} = emqx_retainer_mnesia:page_read(undefined, undefined, Page, Limit),
+    {200, [format_message(Msg) || Msg <- Msgs]}.
 
-with_topic(get, #{bindings := Bindings} = Params) ->
+with_topic(get, #{bindings := Bindings}) ->
     Topic = maps:get(topic, Bindings),
-    lookup(Topic, Params, fun format_detail_message/1);
+    {ok, Msgs} = emqx_retainer_mnesia:page_read(undefined, Topic, 1, 1),
+    case Msgs of
+        [H | _] ->
+            {200, format_detail_message(H)};
+        _ ->
+            {404, #{code => 'NOT_FOUND'}}
+    end;
 
 with_topic(delete, #{bindings := Bindings}) ->
     Topic = maps:get(topic, Bindings),
     emqx_retainer_mnesia:delete_message(undefined, Topic),
     {204}.
 
--spec lookup(undefined | binary(),
-             map(),
-             fun((emqx_types:message()) -> map())) ->
-          {200, map()}.
-lookup(Topic, #{query_string := Qs}, Formatter) ->
-    Page = maps:get(page, Qs, 1),
-    Limit = maps:get(page, Qs, emqx_mgmt:max_row_limit()),
-    {ok, Msgs} = emqx_retainer_mnesia:page_read(undefined, Topic, Page, Limit),
-    {200, format_message(Msgs, Formatter)}.
-
-
-format_message(Messages, Formatter) when is_list(Messages)->
-    [Formatter(Message) || Message <- Messages];
-
-format_message(Message, Formatter) ->
-    Formatter(Message).
-
 format_message(#message{ id = ID, qos = Qos, topic = Topic, from = From
                        , timestamp = Timestamp, headers = Headers}) ->
     #{msgid => emqx_guid:to_hexstr(ID),
@@ -181,12 +175,11 @@ format_message(#message{ id = ID, qos = Qos, topic = Topic, from = From
 
 format_detail_message(#message{payload = Payload} = Msg) ->
     Base = format_message(Msg),
-    EncodePayload = base64:encode(Payload),
-    case erlang:byte_size(EncodePayload) =< ?MAX_BASE64_PAYLOAD_SIZE of
+    case erlang:byte_size(Payload) =< ?MAX_PAYLOAD_SIZE of
         true ->
-            Base#{payload => EncodePayload};
+            Base#{payload => base64:encode(Payload)};
         _ ->
-            Base#{payload => base64:encode(<<"PAYLOAD_TOO_LARGE">>)}
+            Base
     end.
 
 to_bin_string(Data) when is_binary(Data) ->