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

# CrossmintCheckoutCollectionLineItem

> Flutter Final Class

**Final Class**

Line item that mints from a Crossmint collection. Usually built via `CrossmintCheckoutLineItem.collection`.

```dart theme={null}
final class CrossmintCheckoutCollectionLineItem extends CrossmintCheckoutLineItem
```

## Constructors

### CrossmintCheckoutCollectionLineItem

```dart theme={null}
const CrossmintCheckoutCollectionLineItem({
  required this.collectionLocator,
  this.callData,
  this.additionalFields = const <String, Object?>{},
})
```

Creates a collection line item.

## Properties

### collectionLocator

```dart theme={null}
final String collectionLocator
```

Crossmint collection locator (e.g. `"crossmint:<collection-id>"`).

### callData

```dart theme={null}
final Map<String, Object?>? callData
```

Optional call data passed to the on-chain mint (e.g. quantity, metadata overrides).

### additionalFields

```dart theme={null}
final Map<String, Object?> additionalFields
```

Forward-compatibility escape hatch — extra keys appended to the JSON payload. Use for API fields the current SDK version does not model.