diff --git a/apps/emqx_gateway/src/coap/emqx_coap_impl.erl b/apps/emqx_gateway/src/coap/emqx_coap_impl.erl
index 220c25367..9a4c902dc 100644
--- a/apps/emqx_gateway/src/coap/emqx_coap_impl.erl
+++ b/apps/emqx_gateway/src/coap/emqx_coap_impl.erl
@@ -83,7 +83,7 @@ on_gateway_update(Config, Gateway, GwState = #{ctx := Ctx}) ->
             logger:error("Failed to update ~ts; "
                          "reason: {~0p, ~0p} stacktrace: ~0p",
                          [GwName, Class, Reason, Stk]),
-            {error, {Class, Reason}}
+            {error, Reason}
     end.
 
 on_gateway_unload(_Gateway = #{ name := GwName,
diff --git a/apps/emqx_gateway/src/emqx_gateway_api.erl b/apps/emqx_gateway/src/emqx_gateway_api.erl
index d2fd86600..85aad78d2 100644
--- a/apps/emqx_gateway/src/emqx_gateway_api.erl
+++ b/apps/emqx_gateway/src/emqx_gateway_api.erl
@@ -97,7 +97,7 @@ gateway_insta(delete, #{bindings := #{name := Name0}}) ->
             ok ->
                 {204};
             {error, Reason} ->
-                return_http_error(400, Reason)
+                emqx_gateway_http:reason2resp(Reason)
         end
     end);
 gateway_insta(get, #{bindings := #{name := Name0}}) ->
@@ -134,7 +134,7 @@ gateway_insta(put, #{body := GwConf0,
             {ok, Gateway} ->
                 {200, Gateway};
             {error, Reason} ->
-                return_http_error(500, Reason)
+                emqx_gateway_http:reason2resp(Reason)
         end
     end).
 
diff --git a/apps/emqx_gateway/src/emqx_gateway_http.erl b/apps/emqx_gateway/src/emqx_gateway_http.erl
index 228a51b28..b53ccd737 100644
--- a/apps/emqx_gateway/src/emqx_gateway_http.erl
+++ b/apps/emqx_gateway/src/emqx_gateway_http.erl
@@ -311,7 +311,12 @@ return_http_error(Code, Msg) ->
 
 -spec reason2msg({atom(), map()} | any()) -> error | string().
 reason2msg({badconf, #{key := Key, value := Value, reason := Reason}}) ->
-    fmtstr("Bad config value '~s' for '~s', reason: ~s", [Value, Key, Reason]);
+    NValue = case emqx_json:safe_encode(Value) of
+                 {ok, Str} -> Str;
+                 {error, _} -> emqx_gateway_utils:stringfy(Value)
+             end,
+    fmtstr("Bad config value '~s' for '~s', reason: ~s",
+           [NValue, Key, Reason]);
 reason2msg({badres, #{resource := gateway,
                       gateway := GwName,
                       reason := not_found}}) ->
diff --git a/apps/emqx_gateway/src/exproto/emqx_exproto_impl.erl b/apps/emqx_gateway/src/exproto/emqx_exproto_impl.erl
index fac55e24d..2524c1b5d 100644
--- a/apps/emqx_gateway/src/exproto/emqx_exproto_impl.erl
+++ b/apps/emqx_gateway/src/exproto/emqx_exproto_impl.erl
@@ -57,18 +57,19 @@ on_gateway_load(_Gateway = #{ name := GwName,
                               config := Config
                             }, Ctx) ->
     %% XXX: How to monitor it ?
-    %% Start grpc client pool & client channel
-    PoolName = pool_name(GwName),
-    PoolSize = emqx_vm:schedulers() * 2,
-    {ok, PoolSup} = emqx_pool_sup:start_link(
-                      PoolName, hash, PoolSize,
-                      {emqx_exproto_gcli, start_link, []}),
     _ = start_grpc_client_channel(GwName,
                                   maps:get(handler, Config, undefined)
                                  ),
     %% XXX: How to monitor it ?
     _ = start_grpc_server(GwName, maps:get(server, Config, undefined)),
 
+    %% XXX: How to monitor it ?
+    PoolName = pool_name(GwName),
+    PoolSize = emqx_vm:schedulers() * 2,
+    {ok, PoolSup} = emqx_pool_sup:start_link(
+                      PoolName, hash, PoolSize,
+                      {emqx_exproto_gcli, start_link, []}),
+
     NConfig = maps:without(
                  [server, handler],
                  Config#{pool_name => PoolName}
@@ -103,7 +104,7 @@ on_gateway_update(Config, Gateway, GwState = #{ctx := Ctx}) ->
             logger:error("Failed to update ~ts; "
                          "reason: {~0p, ~0p} stacktrace: ~0p",
                          [GwName, Class, Reason, Stk]),
-            {error, {Class, Reason}}
+            {error, Reason}
     end.
 
 on_gateway_unload(_Gateway = #{ name := GwName,
@@ -141,8 +142,11 @@ start_grpc_server(GwName, Options = #{bind := ListenOn}) ->
             console_print("Start ~ts gRPC server on ~p successfully.~n",
                           [GwName, ListenOn]);
         {error, Reason} ->
-            ?ELOG("Failed to start ~ts gRPC server on ~p, reason: ~p",
-                  [GwName, ListenOn, Reason])
+            ?ELOG("Failed to start ~ts gRPC server on ~p, reason: ~0p",
+                  [GwName, ListenOn, Reason]),
+            throw({badconf, #{key => server,
+                              value => Options,
+                              reason => illegal_grpc_server_confs}})
     end.
 
 stop_grpc_server(GwName) ->
diff --git a/apps/emqx_gateway/src/lwm2m/emqx_lwm2m_impl.erl b/apps/emqx_gateway/src/lwm2m/emqx_lwm2m_impl.erl
index 873fbe2c3..0cfb512b5 100644
--- a/apps/emqx_gateway/src/lwm2m/emqx_lwm2m_impl.erl
+++ b/apps/emqx_gateway/src/lwm2m/emqx_lwm2m_impl.erl
@@ -87,7 +87,7 @@ on_gateway_update(Config, Gateway, GwState = #{ctx := Ctx}) ->
             logger:error("Failed to update ~ts; "
                          "reason: {~0p, ~0p} stacktrace: ~0p",
                          [GwName, Class, Reason, Stk]),
-            {error, {Class, Reason}}
+            {error, Reason}
     end.
 
 on_gateway_unload(_Gateway = #{ name := GwName,
diff --git a/apps/emqx_gateway/src/mqttsn/emqx_sn_impl.erl b/apps/emqx_gateway/src/mqttsn/emqx_sn_impl.erl
index 3579bf4bd..a99f81f0a 100644
--- a/apps/emqx_gateway/src/mqttsn/emqx_sn_impl.erl
+++ b/apps/emqx_gateway/src/mqttsn/emqx_sn_impl.erl
@@ -106,7 +106,7 @@ on_gateway_update(Config, Gateway, GwState = #{ctx := Ctx}) ->
             logger:error("Failed to update ~ts; "
                          "reason: {~0p, ~0p} stacktrace: ~0p",
                          [GwName, Class, Reason, Stk]),
-            {error, {Class, Reason}}
+            {error, Reason}
     end.
 
 on_gateway_unload(_Gateway = #{ name := GwName,
diff --git a/apps/emqx_gateway/src/stomp/emqx_stomp_impl.erl b/apps/emqx_gateway/src/stomp/emqx_stomp_impl.erl
index 8e9ae6d1f..47d1899c9 100644
--- a/apps/emqx_gateway/src/stomp/emqx_stomp_impl.erl
+++ b/apps/emqx_gateway/src/stomp/emqx_stomp_impl.erl
@@ -87,7 +87,7 @@ on_gateway_update(Config, Gateway, GwState = #{ctx := Ctx}) ->
             logger:error("Failed to update ~ts; "
                          "reason: {~0p, ~0p} stacktrace: ~0p",
                          [GwName, Class, Reason, Stk]),
-            {error, {Class, Reason}}
+            {error, Reason}
     end.
 
 on_gateway_unload(_Gateway = #{ name := GwName,