The following error is being displayed when attempting to create a SRV record in Plesk:
There is a SRV _sip._tcp.domain.com. record (ID 1271) already.
even though you set it 'udp', not 'tcp'.
This considered as a software issue #PPA-1658.
When you create the record and set the 'Service' drop down meny to 'udp', it is being reset back to 'tcp' when you modify the further parameter.
Pay attention to the record parameters before submitting its creation.