When you configure the presence gateway config on the IM & Presence server, it initially assumes it is a SRV record.
And it auto adds _sip._tcp to the configrued name.

i.e. if you configure purplepi.ie as the gateway address, it will do a SRV lookup for _sip._tcp.purplepi.ie

So configrue with this in mind, (i.e. create your _sip._tcp.<domainname> and add in <domainname>)