What did Support mean by this then?
"At the current time the only you can do is to enable the SRTP for the trunk. If you want this option enable, kindly navigate to SIP Trunks >> Select the provider >> Advanced and enable the option "Switch on Secure RTP (SRTP). Note: The SRTP has to be enabled first through the Settings of the PBX."
Should you need any further assistance, do not hesitate to contact us."