diff --git a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
index 102b95f4e..1b5b6ca9c 100644
--- a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
+++ b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
@@ -708,6 +708,8 @@ typename_to_spec("qos()", _Mod) ->
     #{type => integer, minimum => 0, maximum => 2, example => 0};
 typename_to_spec("{binary(), binary()}", _Mod) ->
     #{type => object, example => #{}};
+typename_to_spec("{string(), string()}", _Mod) ->
+    #{type => object, example => #{}};
 typename_to_spec("comma_separated_list()", _Mod) ->
     #{type => string, example => <<"item1,item2">>};
 typename_to_spec("comma_separated_binary()", _Mod) ->
diff --git a/apps/emqx_prometheus/src/emqx_prometheus.erl b/apps/emqx_prometheus/src/emqx_prometheus.erl
index 91c1f22fc..a66f275f8 100644
--- a/apps/emqx_prometheus/src/emqx_prometheus.erl
+++ b/apps/emqx_prometheus/src/emqx_prometheus.erl
@@ -112,7 +112,7 @@ handle_info({timeout, Timer, ?TIMER_MSG}, State = #{timer := Timer}) ->
 handle_info(_Msg, State) ->
     {noreply, State}.
 
-push_to_push_gateway(Uri, Headers0, JobName) when is_map(Headers0) ->
+push_to_push_gateway(Uri, Headers, JobName) when is_list(Headers) ->
     [Name, Ip] = string:tokens(atom_to_list(node()), "@"),
     JobName1 = emqx_placeholder:preproc_tmpl(JobName),
     JobName2 = binary_to_list(
@@ -124,21 +124,15 @@ push_to_push_gateway(Uri, Headers0, JobName) when is_map(Headers0) ->
 
     Url = lists:concat([Uri, "/metrics/job/", JobName2]),
     Data = prometheus_text_format:format(),
-    Headers = maps:fold(
-        fun(K, V, Acc) ->
-            [{atom_to_list(K), binary_to_list(V)} | Acc]
-        end,
-        [],
-        Headers0
-    ),
     case httpc:request(post, {Url, Headers, "text/plain", Data}, ?HTTP_OPTIONS, []) of
-        {ok, {{"HTTP/1.1", 200, _}, _Headers, _Body}} ->
+        {ok, {{"HTTP/1.1", 200, _}, _RespHeaders, _RespBody}} ->
             ok;
         Error ->
             ?SLOG(error, #{
                 msg => "post_to_push_gateway_failed",
                 error => Error,
-                url => Url
+                url => Url,
+                headers => Headers
             }),
             failed
     end.
diff --git a/apps/emqx_prometheus/src/emqx_prometheus_schema.erl b/apps/emqx_prometheus/src/emqx_prometheus_schema.erl
index da65e02c4..c13d198a2 100644
--- a/apps/emqx_prometheus/src/emqx_prometheus_schema.erl
+++ b/apps/emqx_prometheus/src/emqx_prometheus_schema.erl
@@ -25,7 +25,8 @@
     roots/0,
     fields/1,
     desc/1,
-    translation/1
+    translation/1,
+    convert_headers/1
 ]).
 
 namespace() -> "prometheus".
@@ -54,10 +55,11 @@ fields("prometheus") ->
             )},
         {headers,
             ?HOCON(
-                map(),
+                list({string(), string()}),
                 #{
                     default => #{},
                     required => false,
+                    converter => fun ?MODULE:convert_headers/1,
                     desc => ?DESC(headers)
                 }
             )},
@@ -145,6 +147,17 @@ fields("prometheus") ->
 desc("prometheus") -> ?DESC(prometheus);
 desc(_) -> undefined.
 
+convert_headers(Headers) when is_map(Headers) ->
+    maps:fold(
+        fun(K, V, Acc) ->
+            [{binary_to_list(K), binary_to_list(V)} | Acc]
+        end,
+        [],
+        Headers
+    );
+convert_headers(Headers) when is_list(Headers) ->
+    Headers.
+
 %% for CI test, CI don't load the whole emqx_conf_schema.
 translation(Name) ->
     emqx_conf_schema:translation(Name).