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does anyone know how to dial an elastic SIP trunk from TWIML?

Use Twilio’s Programmable Voice with a SIP Domain and route calls via <Dial><Sip>sip:username@your-sip-domain.sip.twilio.com</Sip></Dial>.

<@1006897684965244938> is username my phone number in twilio? and is the post @ section my termination uri? 

my termination is vapi-sip-xxx-trunk.ptsn.twilio.com

my origination is:
sip:+1XXXXXXXX@sip.vapi.ai

I didn't include:

"outboundAuthenticationPlan": {
      "authUsername": "YOUR_SIP_NUMBER",
      "authPassword": "YOUR_SIP_PASSWORD"
    }

In my create phone number request.

My trunk has only IP Access Control Lists in the termination section as per docs

When I had a candian (access to number). It says the customer you called is not available and then hung up.

In Twilio it says both the parent and child call failed. My TwiML bin post request is:

<?xml version="1.0"?>
<Response>
    <Pause length="9"/>
    <Dial answerOnBridge="true" timeout="15">
        <Sip>sip:+1778XXXXXXX@vapi-sip-xxx-trunk.ptsn.twilio.com</Sip>
    </Dial>
</Response>

I've just had someone test with the traditional add number to the trunk method and it works, so it must be TWIML Code related