curl --request POST \
  --url https://api.upon-ai.com/api/v1/calls/initiate \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "agentId": "agent_01hzexample",
  "fromNumber": "334",
  "toNumber": "+14155550199",
  "trunkName": "Main Sales Trunk",
  "customerName": "Jamie Doe",
  "ignoreE164Validation": true,
  "overrideAgentVersion": 3,
  "customSipHeaders": {
    "X-Campaign": "spring-renewal",
    "X-Case-Id": "case_123"
  },
  "metadata": {
    "customerId": "cust_123",
    "campaign": "renewal"
  },
  "uponai_dynamic_variables": {
    "customer_name": "Jamie",
    "plan_tier": "enterprise"
  },
  "agentOverride": {
    "agent": {
      "voiceId": "elevenlabs-morgan",
      "maxCallDurationMs": 900000
    },
    "llm": {
      "model": "gpt-4.1",
      "beginMessage": "Hello Jamie, this is the virtual team from UponAI."
    }
  }
}
'

{
  "success": true,
  "call_sid": "<string>",
  "call": {
    "success": true,
    "call": {
      "callId": "<string>",
      "callType": "<string>",
      "status": "<string>",
      "agentId": "<string>",
      "agentVersion": 123,
      "metadata": {},
      "optOutSensitiveDataStorage": true,
      "accessToken": "<string>",
      "expiresAt": "2023-11-07T05:31:56Z",
      "webCallUrl": "<string>",
      "uponai_dynamic_variables": {}
    }
  }
}