curl -X POST "https://api.nevatal.com/api/v1/billing/invoices" \
  -H "Authorization: Bearer nvtl_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "patientId": "pat_abc123",
    "items": [
      {
        "description": "Consulta General",
        "procedureId": "proc_general_consult",
        "quantity": 1,
        "unitPrice": 150000,
        "taxRate": 0.19
      }
    ],
    "notes": "Follow-up appointment billing"
  }'

{
  "id": "inv_002",
  "invoiceNumber": "FV-2025-0043",
  "patientId": "pat_abc123",
  "status": "draft",
  "subtotal": 150000,
  "tax": 28500,
  "total": 178500,
  "currency": "COP",
  "createdAt": "2025-03-16T09:00:00Z"
}