In the Telnyx Mission Control Portal, navigate to Voice > TeXML Applications and create a new TeXML app; provide a friendly name, a Voice URL (the HTTP endpoint Telnyx will POST to when a call arrives), and select POST as the method.
Implement your Voice URL endpoint to return XML using Telnyx's TeXML verbs (e.g., <Say>, <Dial>, <Record>, <Gather>); Telnyx sends an application/x-www-form-urlencoded POST with call parameters including CallSid, From, To, and CallStatus.
Set a Status Callback URL on the application to receive asynchronous call lifecycle events (initiated, ringing, answered, completed) as separate POST requests to your webhook endpoint.
Validate incoming webhook signatures: Telnyx API v2 signs webhook payloads using the EdDSA scheme with a public key available in your portal; verify the signature on every incoming request to prevent spoofed callbacks.
Assign phone numbers to the TeXML application in the portal (or via the Telnyx API) so that inbound calls to those numbers invoke your Voice URL.
For dynamic call flows, use the <Redirect> verb to fetch a new TeXML document from a different URL mid-call, or use the Telnyx Call Control API to send commands to a live call identified by its CallControlId.
Known gotchas
Telnyx API v1 used HMAC-SHA256 webhook signing while v2 uses EdDSA; if you migrated from v1 to v2, update your signature verification logic or webhook validation will fail.
TeXML Voice URL requests time out if your endpoint does not respond with valid XML within a few seconds; return a minimal response immediately and use asynchronous processing for slow operations.
The <Gather> verb collects DTMF or speech input and posts results to your action URL; if the caller does not provide input within the timeout, Telnyx calls your action URL with an empty Digits field — handle this case explicitly.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp