> ## Documentation Index
> Fetch the complete documentation index at: https://developer.kalixo.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Open-denomination products

> Order products where you choose the amount within a range.

Most products are **fixed** - they have a single price. **Open-denomination** products let
you choose any amount within an allowed range (for example, a top-up between £5 and £100).

## Identifying open products

Each catalog product includes denomination metadata:

```json theme={"dark"}
{
  "productCode": "10001000000814",
  "name": "Flexible Top-Up",
  "currencyCode": "GBP",
  "denominationType": "open",
  "denominationMinValue": 500,
  "denominationMaxValue": 10000,
  "denominationStep": 100,
  "denominationDefaultValue": 2500
}
```

<ResponseField name="denominationType" type="string">
  `fixed` or `open`.
</ResponseField>

<ResponseField name="denominationMinValue" type="number">
  Minimum amount (minor units) for open products.
</ResponseField>

<ResponseField name="denominationMaxValue" type="number">
  Maximum amount (minor units) for open products.
</ResponseField>

<ResponseField name="denominationStep" type="number">
  Increment the chosen amount must align to.
</ResponseField>

<ResponseField name="denominationDefaultValue" type="number">
  Suggested default amount.
</ResponseField>

## Ordering an open product

Send your chosen amount as the line `price`. It must fall within `[min, max]` and align to `step`.

```bash theme={"dark"}
curl -X POST "https://api.kalixo.io/v2/orders" \
  -H "x-api-key: $KALIXO_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "externalOrderCode": "O-OPEN-1",
    "currency": "GBP",
    "price": 5000,
    "orderProducts": [
      { "productCode": "10001000000814", "price": 5000, "quantity": 1 }
    ]
  }'
```

<Warning>
  Amounts outside the allowed range are rejected with `400 Bad Request`. For **fixed**
  products, the line `price` must exactly match the catalog price.
</Warning>