# cartBuyerIdentityUpdate

Updates the buyer identity for an existing cart.

## Authentication

> **Public Access**: Accessible with the public API key

## Mutation Structure

```graphql
mutation {
  cartBuyerIdentityUpdate(id: String!, buyerIdentity: BuyerIdentityInput) {
    cart {
      # Cart fields
    }
    userErrors {
      # UserError fields
    }
  }
}
```

## Input Arguments

| Argument | Type | Required | Description |
|----------|------|----------|-------------|
| id | String! | Yes | The ID of the cart to update the buyer identity for |
| buyerIdentity | [BuyerIdentityInput](/reference/storefront/v1/inputs/buyer-identity-input) | No | The new buyer identity for the cart |

## Return Type

[CartBuyerIdentityUpdatePayload](/reference/storefront/v1/objects/cart-buyer-identity-update-payload) - Payload returned by the cartBuyerIdentityUpdate mutation. Contains the updated cart and any errors that occurred during the operation.

## Example

```graphql
mutation {
  cartBuyerIdentityUpdate(
    id: "eyJhbGciOiJIUzI1NiJ9..."
    buyerIdentity: {
      email: "customer@example.com"
      firstName: "John"
      lastName: "Doe"
      countryCode: "US"
    }
  ) {
    cart {
      id
      buyerIdentity {
        email
        firstName
        lastName
      }
    }
    userErrors {
      field
      message
    }
  }
}
```

## Related Types

- [CartBuyerIdentityUpdatePayload](/reference/storefront/v1/objects/cart-buyer-identity-update-payload)
- [BuyerIdentityInput](/reference/storefront/v1/inputs/buyer-identity-input)