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Documentation Index

Fetch the complete documentation index at: https://docs.vobiz.ai/llms.txt

Use this file to discover all available pages before exploring further.

This guide shows how to integrate Retell AI with Vobiz using the API for automated outbound calling - ideal for developers building applications that trigger AI calls programmatically.
Prefer a visual dashboard? Check out the dashboard setup guide for a no-code integration method.

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Prerequisites

Get Vobiz credentials:

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Step 1: Get your API key

  1. Go to Retell Dashboard → Settings → API Keys.
  2. Click Create API Key.
  3. Copy the key (it starts with key_).
Keep this key secret - never commit it to git or share publicly. Store it securely in environment variables.

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Step 2: List available agents

Retrieve all agents to get the agent_id you’ll use for calls: 
curl "https://api.retellai.com/list-agents" \
  -H "Authorization: Bearer key_abc123xyz789example"
Example response: 
[
  {
    "agent_id": "agent_abc123example",
    "agent_name": "Customer Support Agent",
    "voice_id": "11labs-Rachel",
    "language": "en-US"
  }
]
What to extract:
  • agent_id - use this when making calls
  • agent_name - human-readable label
  • voice_id - the voice the agent uses
Copy the agent_id for the agent you want to use.

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Step 3: Configure phone number with SIP trunk

Add your Vobiz phone number and SIP trunk configuration to Retell: 
curl "https://api.retellai.com/create-phone-number" \
  -X POST \
  -H "Authorization: Bearer key_abc123xyz789example" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_number": "+1234567890",
    "phone_number_type": "custom",
    "nickname": "Vobiz Main Line",
    "outbound_agent_id": "agent_abc123example",
    "sip_outbound_trunk_config": {
      "termination_uri": "abc123.sip.vobiz.ai",
      "transport": "TCP",
      "auth_username": "your_username",
      "auth_password": "your_password"
    }
  }'
Required fields:
FieldDescription
phone_numberYour Vobiz number in E.164 format
phone_number_typeMust be "custom" for SIP trunks
outbound_agent_idAgent ID from Step 2
sip_outbound_trunk_config.termination_uriVobiz SIP domain (without the sip: prefix)
sip_outbound_trunk_config.transport"TCP" (recommended)
sip_outbound_trunk_config.auth_usernameVobiz trunk username
sip_outbound_trunk_config.auth_passwordVobiz trunk password
Get your Vobiz credentials from Vobiz Console → Trunks → your trunk.

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Step 4: Make an outbound call

Trigger an outbound AI call programmatically: 
curl "https://api.retellai.com/v2/create-phone-call" \
  -X POST \
  -H "Authorization: Bearer key_abc123xyz789example" \
  -H "Content-Type: application/json" \
  -d '{
    "from_number": "+1234567890",
    "to_number": "+10987654321",
    "agent_id": "agent_abc123example"
  }'
Required parameters:
FieldDescription
from_numberYour configured Vobiz number (caller ID)
to_numberDestination number to call (E.164 format)
agent_idWhich agent to use for the call
Example response: 
{
  "call_id": "call_abc123xyz789",
  "call_status": "registered",
  "from_number": "+1234567890",
  "to_number": "+10987654321",
  "direction": "outbound"
}
Call status values:
  • registered - call initiated
  • ringing - phone is ringing
  • ongoing - call connected
  • ended - call finished
Call initiated! The destination phone will ring, and when answered, the AI agent will speak.

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Troubleshooting

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401 Unauthorized

Invalid API key.

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”Phone number not found”

Phone number not configured in Retell.
  • Run Step 3 to add the phone number with the SIP trunk.
  • Verify the number format is E.164.

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Call fails immediately

Possible causes:
  1. Wrong SIP credentials - verify Vobiz username/password at Vobiz Console.
  2. Wrong transport type - try "UDP" instead of "TCP" in the trunk config.
  3. Incorrect SIP domain - must be the exact Vobiz domain (for example, abc123.sip.vobiz.ai); do not include the sip: prefix.
  4. Insufficient balance - check your Vobiz account has credits at Vobiz Console. See account balance.

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Agent doesn’t speak

Agent not configured or not published.
  • Ensure the agent is published in Retell Dashboard → Agents.
  • Check the agent has a voice configured.
  • Verify the agent ID matches the phone number config.

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Quick reference

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API endpoints

Base URL: https://api.retellai.com Authentication: Authorization: Bearer YOUR_API_KEY
EndpointMethodPurpose
/list-agentsGETList all agents
/list-phone-numbersGETList configured numbers
/create-phone-numberPOSTAdd phone number with SIP trunk
/v2/create-phone-callPOSTMake outbound call
/get-call/{call_id}GETGet call details

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Complete call flow

# 1. List agents
curl "https://api.retellai.com/list-agents" \
  -H "Authorization: Bearer key_YOUR_KEY_HERE"

# 2. Configure phone number (one-time)
curl "https://api.retellai.com/create-phone-number" \
  -X POST \
  -H "Authorization: Bearer key_YOUR_KEY_HERE" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_number": "+1234567890",
    "phone_number_type": "custom",
    "outbound_agent_id": "agent_YOUR_AGENT_ID",
    "sip_outbound_trunk_config": {
      "termination_uri": "abc123.sip.vobiz.ai",
      "transport": "TCP",
      "auth_username": "your_username",
      "auth_password": "your_password"
    }
  }'

# 3. Make a call
curl "https://api.retellai.com/v2/create-phone-call" \
  -X POST \
  -H "Authorization: Bearer key_YOUR_KEY_HERE" \
  -H "Content-Type: application/json" \
  -d '{
    "from_number": "+1234567890",
    "to_number": "+10987654321",
    "agent_id": "agent_YOUR_AGENT_ID"
  }'

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Resources

Your Retell AI agents can now make outbound calls through Vobiz programmatically - perfect for automated campaigns and application integrations.