Configuration

The PubSub node must be created and configured beforehand:

Create node
<iq type='set'
    to='pubsub.coffeebean.local'
    id='create1'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub'>
    <create node='message_sink'/>
  </pubsub>
</iq>

After that is done, you need to add SessionManager as a publisher:

Add sess-man as publisher
<iq type='set'
    to='pubsub.coffeebean.local'
    id='ent2'>
  <pubsub xmlns='http://jabber.org/protocol/pubsub#owner'>
    <affiliations node='message_sink'>
      <affiliation jid='sess-man@coffeebean.local' affiliation='publisher'/>
    </affiliations>
  </pubsub>
</iq>

Finally, the AMP plugin must be configured as well

init.properties configuration
sess-man/plugins-conf/amp/msg-pubsub-jid=pubsub.coffeebean.local
sess-man/plugins-conf/amp/msg-pubsub-node=message_sink
sess-man/plugins-conf/amp/msg-pubsub-publisher=sess-man@coffeebean.local

Of course be sure that AMP plugin is in your --sm-plugins line.