diff --git a/apps/emqx_authz/src/emqx_authz_api_mnesia.erl b/apps/emqx_authz/src/emqx_authz_api_mnesia.erl
index 1f33c7a1f..45a813f1d 100644
--- a/apps/emqx_authz/src/emqx_authz_api_mnesia.erl
+++ b/apps/emqx_authz/src/emqx_authz_api_mnesia.erl
@@ -171,6 +171,8 @@ schema("/authorization/sources/built-in-database/username/:username") ->
                   #{ 204 => <<"Deleted">>
                    , 400 => emqx_dashboard_swagger:error_codes(
                               [?BAD_REQUEST], <<"Bad username">>)
+                   , 404 => emqx_dashboard_swagger:error_codes(
+                              [?NOT_FOUND], <<"Username Not Found">>)
                    }
             }
      };
@@ -207,6 +209,8 @@ schema("/authorization/sources/built-in-database/clientid/:clientid") ->
                   #{ 204 => <<"Deleted">>
                    , 400 => emqx_dashboard_swagger:error_codes(
                               [?BAD_REQUEST], <<"Bad clientid">>)
+                   , 404 => emqx_dashboard_swagger:error_codes(
+                              [?NOT_FOUND], <<"ClientID Not Found">>)
                    }
             }
      };
@@ -315,8 +319,8 @@ clients(get, #{query_string := QueryString}) ->
                                         ?ACL_TABLE, ?ACL_CLIENTID_QSCHEMA, ?QUERY_CLIENTID_FUN),
     emqx_mgmt_util:generate_response(Response);
 clients(post, #{body := Body}) when is_list(Body) ->
-    lists:foreach(fun(#{<<"clientid">> := Clientid, <<"rules">> := Rules}) ->
-                          emqx_authz_mnesia:store_rules({clientid, Clientid}, format_rules(Rules))
+    lists:foreach(fun(#{<<"clientid">> := ClientID, <<"rules">> := Rules}) ->
+                          emqx_authz_mnesia:store_rules({clientid, ClientID}, format_rules(Rules))
                   end, Body),
     {204}.
 
@@ -332,31 +336,41 @@ user(get, #{bindings := #{username := Username}}) ->
             }
     end;
 user(put, #{bindings := #{username := Username},
-              body := #{<<"username">> := Username, <<"rules">> := Rules}}) ->
+            body := #{<<"username">> := Username, <<"rules">> := Rules}}) ->
     emqx_authz_mnesia:store_rules({username, Username}, format_rules(Rules)),
     {204};
 user(delete, #{bindings := #{username := Username}}) ->
-    emqx_authz_mnesia:delete_rules({username, Username}),
-    {204}.
+    case emqx_authz_mnesia:get_rules({username, Username}) of
+        not_found ->
+            {404, #{code => <<"NOT_FOUND">>, message => <<"Username Not Found">>}};
+        {ok, _Rules} ->
+            emqx_authz_mnesia:delete_rules({username, Username}),
+            {204}
+    end.
 
-client(get, #{bindings := #{clientid := Clientid}}) ->
-    case emqx_authz_mnesia:get_rules({clientid, Clientid}) of
+client(get, #{bindings := #{clientid := ClientID}}) ->
+    case emqx_authz_mnesia:get_rules({clientid, ClientID}) of
         not_found -> {404, #{code => <<"NOT_FOUND">>, message => <<"Not Found">>}};
         {ok, Rules} ->
-            {200, #{clientid => Clientid,
+            {200, #{clientid => ClientID,
                     rules => [ #{topic => Topic,
                                  action => Action,
                                  permission => Permission
                                 } || {Permission, Action, Topic} <- Rules]}
             }
     end;
-client(put, #{bindings := #{clientid := Clientid},
-              body := #{<<"clientid">> := Clientid, <<"rules">> := Rules}}) ->
-    emqx_authz_mnesia:store_rules({clientid, Clientid}, format_rules(Rules)),
+client(put, #{bindings := #{clientid := ClientID},
+              body := #{<<"clientid">> := ClientID, <<"rules">> := Rules}}) ->
+    emqx_authz_mnesia:store_rules({clientid, ClientID}, format_rules(Rules)),
     {204};
-client(delete, #{bindings := #{clientid := Clientid}}) ->
-    emqx_authz_mnesia:delete_rules({clientid, Clientid}),
-    {204}.
+client(delete, #{bindings := #{clientid := ClientID}}) ->
+    case emqx_authz_mnesia:get_rules({clientid, ClientID}) of
+        not_found ->
+            {404, #{code => <<"NOT_FOUND">>, message => <<"ClientID Not Found">>}};
+        {ok, _Rules} ->
+            emqx_authz_mnesia:delete_rules({clientid, ClientID}),
+            {204}
+    end.
 
 all(get, _) ->
     case emqx_authz_mnesia:get_rules(all) of
@@ -453,8 +467,8 @@ format_result([{username, Username}, {rules, Rules}]) ->
                    permission => Permission
                   } || {Permission, Action, Topic} <- Rules]
      };
-format_result([{clientid, Clientid}, {rules, Rules}]) ->
-    #{clientid => Clientid,
+format_result([{clientid, ClientID}, {rules, Rules}]) ->
+    #{clientid => ClientID,
       rules => [ #{topic => Topic,
                    action => Action,
                    permission => Permission