Telnyx

A 4-digit identifier prepended to outbound calls to differentiate multiple SIP connections sharing the same IP address.

Dial string format

[tech_prefix][destination_number]

Example: Tech prefix 1234 + destination +18005678912 = 123418005678912

{
  "inbound": {
    "sip_subdomain_receive_settings": "from_anyone"
  },
  "outbound": {
    "tech_prefix_enabled": true
  }
}

Tech prefix value is assigned by Telnyx and visible in the connection settings.

The PBX or SIP client must prepend the tech prefix to all outbound calls on the trunk.

Condition	Result
Correct tech prefix included	Call authenticated
Missing or incorrect prefix	`407 Proxy Authentication Required`

For connections sharing an IP address:

⌘I