diff --git a/apps/iot/src/endpoint/iot_zd_endpoint.erl b/apps/iot/src/endpoint/iot_zd_endpoint.erl
index a4c0d96..2126fee 100644
--- a/apps/iot/src/endpoint/iot_zd_endpoint.erl
+++ b/apps/iot/src/endpoint/iot_zd_endpoint.erl
@@ -206,7 +206,7 @@ create_postman(Opts) ->
     Port = proplists:get_value(port, Opts),
     Username = proplists:get_value(username, Opts),
     Password = proplists:get_value(password, Opts),
-    Topic = proplists:get_value(topic, Opts),
+    Topic0 = proplists:get_value(topic, Opts),
     Qos = proplists:get_value(qos, Opts),
 
     Node = atom_to_binary(node()),
@@ -225,7 +225,7 @@ create_postman(Opts) ->
         {retry_interval, 5000}
     ],
 
-    mqtt_postman:start_link(PostmanOpts, Topic, Qos).
+    mqtt_postman:start_link(PostmanOpts, list_to_binary(Topic0), Qos).
 
 -spec do_post(PostmanPid :: pid(), NorthData :: #north_data{}) -> no_return().
 do_post(PostmanPid, #north_data{id = Id, location_code = LocationCode, dynamic_location_code = DynamicLocationCode, fields = Fields, timestamp = Timestamp}) when is_pid(PostmanPid) ->
diff --git a/apps/iot/src/postman/mqtt_postman.erl b/apps/iot/src/postman/mqtt_postman.erl
index e73bb1f..d24f31e 100644
--- a/apps/iot/src/postman/mqtt_postman.erl
+++ b/apps/iot/src/postman/mqtt_postman.erl
@@ -32,7 +32,7 @@
 %% @doc Spawns the server and registers the local name (unique)
 -spec(start_link(Opts :: list(), Topic :: binary(), Qos :: integer()) ->
     {ok, Pid :: pid()} | ignore | {error, Reason :: term()}).
-start_link(Opts, Topic, Qos) when is_list(Opts), is_binary(Topic), Qos == 0; Qos == 1; Qos == 2 ->
+start_link(Opts, Topic, Qos) when is_list(Opts) andalso is_binary(Topic) andalso (Qos == 0 orelse Qos == 1 orelse Qos == 2) ->
     gen_server:start_link(?MODULE, [Opts, Topic, Qos], []).
 
 %%%===================================================================