curl --request POST \
  --url https://api.rntor.com/v1/invoices/{id}/items \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'X-Client-ID: <api-key>' \
  --data '
{
  "description": "<string>",
  "quantity": 123,
  "unit_price": 123
}
'

{
  "data": {
    "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "invoice_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "description": "<string>",
    "quantity": 123,
    "unit_price": 123,
    "total": 123
  },
  "meta": {
    "request_id": "req_abc123def456",
    "timestamp": "2024-01-15T10:30:00Z"
  }
}