Add Cart Line Items

Adds line item to the *Cart*. **Usage Notes** To add a custom item use `custom_items`. Note that images are not supported for custom items; the `image_url` field is accepted but does not render on the storefront. If a product has modifiers, omit the `variant_id` and instead use the `option_selections` array to describe both the **variant** and the **modifier** selections. To prevent lost updates due to concurrent requests overriding changes made by others, it is recommended to enable optimistic concurrency control by including the `version` field in the request payload. If the provided version does not match the version on the server, a conflict error will be returned, which the client can handle accordingly. **Overridable fields** When adding a line item, you can override the following catalog values: | Field | Description | |-|-| | `list_price` | Override the product's price. By default, overriding a product's `list_price` makes it ineligible for V3 product-level promotions. In **Store Settings** under **Promotions and Coupons** in the control panel, you can change this behavior to allow promotions on overridden prices. | | `name` | Override the product name. Useful for locale-specific product names. | | `option_selections.name` | Override the name of an option or modifier selection. Useful for locale-specific option labels. | | `option_selections.value` | Override the value of an option or modifier selection. Useful for locale-specific option values. |