# Update a cart item (/api/carts/update-cart-item)

`POST https://api.comecero.com/api/v1/carts/{cart_id}/items/{item_id}`

Changes the quantity, `meta` or (secret and trusted tokens only) `reference_price` of an item. A limited token sending `reference_price` or `reference_currency` gets `403` (error `m82tixT`). An item that is part of a bundle cannot be changed (`400`, error `kx3Bq7T`): delete it and add the bundle again. Any token type may call it; a limited token only for a bound cart. A closed cart is `422`.

## Parameters

- `cart_id` (path, required): The id of the cart.
- `item_id` (path, required): The id of the item. For a product, the product_id.
- `expand` (query): Comma-separated child objects to return in full instead of as a URL, for example `customer,payments`. Use dot notation for nested objects (`items.product`), up to four levels deep. A single object takes up to 12 paths; a list takes up to 2, applied to every item. Extra paths are dropped without an error. See [Expanding objects](https://docs.comecero.com/docs/basic-concepts/expanding-objects).
- `formatted` (query): When `true`, the object also has a `formatted` child with amounts and dates as display text in the shopper's language and currency (for example `$19.99` or `November 7, 2026`). The default is `false`. See [Localized formatting](https://docs.comecero.com/docs/basic-concepts/localized-formatting).

Request body: the `cart_item_request` schema.

Responses: 200, 400, 401, 403, 404, 422, 500.

Full schemas: operation `update_cart_item` in /openapi.json.