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  1. In Twilio Elastic SIP Trunking, add an Origination SIP URI in the form sip:<platform-sip-fqdn>;transport=tcp and assign the DID to the trunk.
  2. In the platform, enter the exact +E.164 DID and select Provider source IPs.
  3. Do not use platform inbound digest. Twilio credential lists authenticate customer-to-Twilio termination, not Twilio-to-platform origination.
Allow every Twilio regional signaling CIDR for failover:
Twilio documents UDP/TCP signaling on port 5060 and TLS on 5061. The list above is for signaling; do not substitute Twilio media ranges. For outbound calls, configure the Twilio termination domain and a Twilio credential list separately. A Twilio termination host normally follows <name>.pstn.twilio.com; do not paste an Origination SIP URI into that field.

Two call directions — conceptual diagram

These examples show the relevant settings; the layout can differ in your provider’s current console.
Twilio Elastic SIP Trunking Termination page with the Termination SIP URI field and IP Access Control Lists

Configuration example — Twilio's Termination page — where the outbound SIP URI and IP ACLs live

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Troubleshooting

Outbound calls don’t connect, but inbound works — check the Termination SIP URI first for a stray space or a copy-paste error; it must be exact (<name>.pstn.twilio.com), with no extra whitespace. Twilio also publishes localized termination URIs — use the one closest to your own region rather than the default global host before you start changing credentials. International calls fail or are rejected — open Voice → Settings → Geo permissions in Twilio Console and allow the destination countries and number ranges you need. These permissions apply to both Programmable Voice and Elastic SIP Trunking. Twilio’s current instructions.

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Validate

Call the Twilio DID externally. Confirm a new inbound record, correct assistant routing, and two-way audio. A Twilio call log without a corresponding platform inbound call is not proof of delivery. Sources: Twilio signaling IPs, Twilio Elastic SIP Trunking. Accessed 22 August 2026.