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Documentation Index

Fetch the complete documentation index at: https://docs.voiceflow.com/llms.txt

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In some regions, automated outbound calls without consent may violate local regulations. You are responsible for ensuring compliance with all relevant laws.
Outbound calling lets your agent initiate phone calls programmatically. You can use this to automate voice interactions like welcome calls, appointment reminders, or follow-ups, triggered from tools like Zapier or your own backend scripts. Outbound calling is supported for Twilio, Vonage, and Telnyx phone numbers. Voiceflow phone numbers currently don’t support outbound calling.

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Making an outbound call

To trigger an outbound call, send a POST request to your agent’s outbound API endpoint. You can find this endpoint by opening Phone numbers in the sidebar, then clicking View in the Outbound call API column for your number. The modal displays a ready-to-use curl command with your agent’s endpoint and required headers. You can also test the call directly from this modal by entering a phone number and clicking Call.

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API reference

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Endpoint

POST https://runtime-api.voiceflow.com/v1/phone-number/<PHONE_NUMBER_ID>/outbound

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Headers

HeaderValue
AuthorizationYour Dialog Manager API key
Content-Typeapplication/json

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Request body

{
  "to": "+15551234567",
  "variables": {
    "user_name": "Jane",
    "account_type": "Premium"
  },
  "amd": true
}
FieldDescription
toThe phone number to call in E.164 format (eg: +15551234567).
variablesOptional. A JSON object containing variables to inject when the call starts.
amdOptional. Set to true to enable answering machine detection.

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Concurrency limits

Outbound calls share the same concurrency pool as inbound calls. The number of simultaneous calls you can make depends on your plan limits.