{
  "contacts": [
    {
      "externalId": "lead-123",
      "email": "sarah.chen@techstartup.io",
      "firstName": "Sarah",
      "lastName": "Chen",
      "linkedinUrl": "https://linkedin.com/in/sarahchen"
    },
    {
      "externalId": "lead-456",
      "email": "new.prospect@unknown.com"
    }
  ]
}

{
  "results": [
    {
      "externalId": "lead-123",
      "crmId": "contact_8f3k2j",
      "properties": {
        "leadScore": 85,
        "lifecycleStage": "MQL",
        "lastActivityDate": "2024-01-15T14:30:00Z"
      }
    }
  ]
}