urn:xmpp:carbons:2 not showing up in list installed features

I have tried to install mod_message_carbon. I have

compiled mod_message_carbon using build.sh as documented,
copied mod_message_carbon.beam to /usr/lib/ejabberd/ebin (on Debian),
added {mod_message_carbon, []} to modules in /etc/ejabberd/ejabberd.cfg,
restarted ejabberd using service ejabberd restart.

I hoped to find my messages carbon copied to my other clients, but sadly, I didn't. I have checked /var/log/ejabberd/ejabberd.log for anything that might have gone wrong. I can't find anything that seems to.

I have executed the command below, copied from the XEP-0280's specification. Yes, I changed it to my details.

<iq xmlns='jabber:client'
    type='get'
    from='romeo@montague.net/orchard'
    id='info1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

My server responded with a nice list, but sadly it did no contain urn:xmpp:carbons:2 as specified in the page linked to above.

What can I do to make it work?

abhinavsingh / mod_message_carbon

urn:xmpp:carbons:2 not showing up in list installed features #3