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

# Update Item Quantity

> Updates the quantity of an item in the cart

## Overview

Updates the quantity of an existing item in the cart. Set quantity to 0 to remove the item.

## Authentication

<Card>
  <ParamField header="x-firmly-authorization" type="string" required>
    Device authentication token from browser session
  </ParamField>
</Card>

## Path Parameters

<ParamField path="domain" type="string" required>
  Merchant domain (e.g., `staging.luma.gift`)
</ParamField>

<ParamField path="sku" type="string" required>
  Product SKU to update (e.g., `WS12-XS-Orange`)
</ParamField>

## Request Body

<ParamField body="quantity" type="number" required>
  New quantity (minimum: 0, set to 0 to remove)
</ParamField>

<ParamField body="variant_handles" type="array">
  List of variant handles if required by the merchant
</ParamField>

## Query Parameters

<ParamField query="fast_mode" default="false" type="string">
  Set to `true` for faster response with potentially cached data
</ParamField>

## Response

Returns the updated shopping cart.

### Response Fields

Same as [Get Cart](/api-reference/simple-cart-api/cart/get-cart#response-fields) response.

<RequestExample>
  ```bash cURL theme={null}
  curl --request PUT \
    --url https://api.firmly.work/api/v1/domains/staging.luma.gift/cart/line-items/WS12-XS-Orange \
    --header 'x-firmly-authorization: YOUR_TOKEN' \
    --header 'Content-Type: application/json' \
    --data '{"quantity": 2}'
  ```

  ```javascript JavaScript theme={null}
  const response = await fetch('https://api.firmly.work/api/v1/domains/staging.luma.gift/cart/line-items/WS12-XS-Orange', {
    method: 'PUT',
    headers: {
      'x-firmly-authorization': 'YOUR_TOKEN',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      quantity: 2
    })
  });

  const cart = await response.json();
  ```

  ```python Python theme={null}
  import requests

  response = requests.put(
      'https://api.firmly.work/api/v1/domains/staging.luma.gift/cart/line-items/WS12-XS-Orange',
      headers={
          'x-firmly-authorization': 'YOUR_TOKEN',
          'Content-Type': 'application/json'
      },
      json={
          'quantity': 2
      }
  )

  cart = response.json()
  ```
</RequestExample>

<ResponseExample>
  ```json Success Response theme={null}
  {
    "cart_id": "1e43868c-d4a5-418c-bd6b-5fff043550d2",
    "platform_id": "example",
    "shop_id": "staging.luma.gift",
    "display_name": "Luma Store",
    "line_items": [
      {
        "line_item_id": "1ee530e1-063d-4e07-afb2-e7e65245977e",
        "platform_line_item_id": "4df9941b-bd06-4495-8759-61c6145dc408",
        "sku": "WS12-XS-Orange",
        "base_sku": "WS12",
        "quantity": 2,
        "description": "Radiant Tee - Orange XS",
        "price": {
          "currency": "USD",
          "value": 22.00,
          "symbol": "$",
          "number": 2200
        },
        "line_price": {
          "currency": "USD",
          "value": 44.00,
          "symbol": "$",
          "number": 4400
        },
        "msrp": {
          "currency": "USD",
          "value": 22.00,
          "symbol": "$",
          "number": 2200
        },
        "image": {
          "url": "https://cdn.staging.luma.gift/products/radiant-tee/orange.jpg"
        },
        "requires_shipping": true
      }
    ],
    "sub_total": {
      "currency": "USD",
      "value": 1739.98,
      "symbol": "$",
      "number": 173998
    },
    "shipping_total": {
      "currency": "USD",
      "value": 0,
      "symbol": "$",
      "number": 0
    },
    "tax": {
      "currency": "USD",
      "value": 4.40,
      "symbol": "$",
      "number": 440
    },
    "total": {
      "currency": "USD",
      "value": 48.40,
      "symbol": "$",
      "number": 4840
    },
    "payment_method_options": [
      {
        "type": "CreditCard",
        "wallet": "user"
      }
    ]
  }
  ```

  ```json Item Removed (quantity: 0) theme={null}
  {
    "cart_id": "1e43868c-d4a5-418c-bd6b-5fff043550d2",
    "platform_id": "example",
    "shop_id": "staging.luma.gift",
    "display_name": "Luma Store",
    "line_items": [],
    "sub_total": {
      "currency": "USD",
      "value": 0,
      "symbol": "$",
      "number": 0
    },
    "tax": {
      "currency": "USD",
      "value": 0,
      "symbol": "$",
      "number": 0
    },
    "total": {
      "currency": "USD",
      "value": 0,
      "symbol": "$",
      "number": 0
    },
    "payment_method_options": [
      {
        "type": "CreditCard",
        "wallet": "user"
      }
    ]
  }
  ```
</ResponseExample>

## Error Responses

### 400 Bad Request

Missing or invalid authentication header

### 404 Not Found

Product not found in the cart

### 409 Conflict

Not enough stock available for the requested quantity

### 422 Unprocessable Entity

Invalid request body format