ejabberd - not able to send a custom IQ to another user - xmpp

Question

I'm writing a custom ejabberd module. When I send a custom IQ stanza using strophe js, ejabberd processes the request and returns the result IQ back to the sender.
Below is the IQ request I send using strophe js,
connection.sendIQ($iq({
to: 'john#localhost',
type: 'set',
id: 'abc1234567890'
})
.c('query', {
xmlns: 'jabber:iq:custom_module',
msg_id: 'xyz9876543210'
})
.tree());
and this is the ejabberd module code,
-module(mod_custom_module).
-behaviour(gen_mod).
-define(NS_CUSTOM_MODULE, <<"jabber:iq:custom_module">>).
-export([start/2, stop/1, depends/2, mod_options/1, process_sm_iq/1, decode_iq_subel/1]).
-include("xmpp.hrl").
-include("logger.hrl").
-include("ejabberd_sql_pt.hrl").
start(_Host, _Opts) ->
gen_iq_handler:add_iq_handler(ejabberd_sm, _Host, ?NS_CUSTOM_MODULE, ?MODULE, process_sm_iq, one_queue).
stop(_Host) ->
gen_iq_handler:remove_iq_handler(ejabberd_sm, _Host, ?NS_CUSTOM_MODULE).
depends(_Host, _Opts) ->
[].
mod_options(_Host) ->
[].
-spec decode_iq_subel(xmpp_element()) -> xmpp_element();
(xmlel()) -> xmlel().
decode_iq_subel(El) ->
El.
-spec process_sm_iq(iq()) -> iq().
process_sm_iq(#iq{from = _From, to = _To, sub_els = _sub_els} = IQ) ->
% My module actions here...
[First | Rest] = _sub_els,
xmpp:make_iq_result(IQ, First).
After processing the IQ, I also want to notify the other user 'john#localhost' about the custom event. I tried to do this using ejabberd_router:route/3, but it did not work.
I don't know what I am doing wrong.
Update
When I use the following code, the other user is not receiving stanza.
NewIQ = #iq{id = _Id, type = result, to = _To, from = _From, sub_els = _sub_els},
ejabberd_router:route(xmpp:set_from_to(NewIQ, _From, _To)),
% or ejabberd_router:route(NewIQ),
% or ejabberd_sm:route(NewIQ),
And when I checked the debug console, it is showing the following message in it. Not sure whether this is relevant as it is just a debug type message and there is no other failure error message.
17:07:47.173 [debug] Dropping packet to unavailable resource:
#iq{id = <<"abc1234567890">>,type = result,lang = <<>>,
from = #jid{user = <<"nikhil">>,server = <<"localhost">>,
resource = <<"49230572059507447681762">>,luser = <<"nikhil">>,
lserver = <<"localhost">>,
lresource = <<"49230572059507447681762">>},
to = #jid{user = <<"john">>,server = <<"localhost">>,
resource = <<>>,luser = <<"john">>,
lserver = <<"localhost">>,lresource = <<>>},
sub_els = [#xmlel{name = <<"query">>,
attrs = [{<<"xmlns">>,<<"jabber:iq:custom_module">>},
{<<"msg_id">>,<<"xyz9876543210">>}],
children = []}],
meta = #{}}

Answer 1

Try this function. It sends a headline message to the destination account with some details about the original IQ.
process_sm_iq(#iq{from = From, to = To, sub_els = SubEls} = IQ) ->
[First | Rest] = SubEls,
MsgId = fxml:get_tag_attr_s(<<"msg_id">>, First),
Subject = "Event alert",
Body = "An IQ was received by custom_module with msg_id: "++MsgId,
Packet = #message{from = From,
to = To,
type = headline,
body = xmpp:mk_text(Body),
subject = xmpp:mk_text(Subject)},
ejabberd_router:route(Packet),
xmpp:make_iq_result(IQ, First).