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API ReferenceEndpointsCartUpdate cart item (Public API)

Update cart item (Public API)

Supports Idempotency-Key header for safe retries.

PATCH
/v1/cart/{cartId}/items/{itemId}

Authorization

AuthorizationBearer <token>

Admin API key (server-to-server). Issue via the dashboard at Settings → API keys. Plain-text key is shown once — store in a secret manager. Format: Authorization: Bearer brainerce_xxxxxxxxx.

In: header

Path Parameters

cartIdstring

Cart ID

itemIdstring

Cart Item ID

Header Parameters

Idempotency-Key?string

Client-supplied key (a UUID v4 is the recommended form, max 255 characters) that makes this mutation safe to retry.

  • Replay window: 24 hours. The first response for a key is cached; a retry inside the window with the same request body returns the original status and body without re-running the handler.
  • Reusing a key with a different body returns 409 Conflict with code: "IDEMPOTENCY_KEY_REUSED". The request fingerprint (method + path + body hash) is compared against the stored one; a mismatch is refused rather than served the old response.
  • Keys are scoped to the calling credential and store — two API keys may safely use the same key value.
  • Error responses are cached too, so a retry of a request that failed validation returns the same 400 immediately.
  • Sending this header on a GET returns 400 with code: "IDEMPOTENCY_KEY_NOT_SUPPORTED" — GETs are already idempotent.
  • Support is per-route and this parameter is the authoritative signal: a key sent to a route that does not declare it is accepted and silently ignored.

See /docs/api/idempotency.

Lengthlength <= 255

Request Body

quantity?integer

New quantity (0 to 1000). Setting quantity: 0 removes the line, same as DELETE.

Range0 <= value <= 1000
notes?string

New shopper-facing note for this line.

selections?array<ModifierSelectionDto>

New modifier selections. PRD §7.2.3: present means REPLACE all existing selections on this line. Omit to keep the existing selections unchanged.

nestedByModifierId?object

New nested combo selections, keyed by parent modifier id. Same REPLACE semantics as selections.

curl -X PATCH "https://api.brainerce.com/api/v1/cart/string/items/string" \  -H "Idempotency-Key: string" \  -H "Content-Type: application/json" \  -d '{}'
{
  "id": "clx1a2b3c4d5e6f7g8h9",
  "sessionToken": "cs_7d9f2a1b3c4e5f60",
  "customerId": "clx1a2b3c4d5e6f7g8h9",
  "status": "ACTIVE",
  "currency": "USD",
  "notes": "Leave at the door",
  "analyticsClientId": "clx1a2b3c4d5e6f7g8h9",
  "analyticsSessionId": "clx1a2b3c4d5e6f7g8h9",
  "subtotal": "59.80",
  "discountAmount": "5.00",
  "ruleDiscountAmount": "5.00",
  "promoDiscountTotal": "0.00",
  "couponCode": "WELCOME10",
  "appliedDiscounts": [
    {
      "ruleId": "clx1a2b3c4d5e6f7g8h9",
      "ruleName": "Summer sale",
      "type": "ORDER_DISCOUNT",
      "discountAmount": "10.00",
      "description": "10% off orders over 200"
    }
  ],
  "nudges": [
    {
      "ruleId": "clx1a2b3c4d5e6f7g8h9",
      "text": "Add 20.00 more for free shipping",
      "type": "AMOUNT_NEEDED",
      "amountNeeded": "20.00",
      "quantityNeeded": 1
    }
  ],
  "items": [
    {
      "id": "clx1a2b3c4d5e6f7g8h9",
      "productId": "clx1a2b3c4d5e6f7g8h9",
      "variantId": "clx1a2b3c4d5e6f7g8h9",
      "quantity": 2,
      "unitPrice": "29.90",
      "currentUnitPrice": "31.90",
      "priceChanged": true,
      "priceDelta": "2.00",
      "priceDirection": "increased",
      "isAvailable": true,
      "unavailableReason": "PRODUCT_DRAFT",
      "discountAmount": "0.00",
      "promoDiscountAmount": "0.00",
      "promoSource": "BUNDLE",
      "promoSourceId": "clx1a2b3c4d5e6f7g8h9",
      "notes": "Gift wrap please",
      "metadata": {},
      "customizations": {},
      "product": {
        "id": "clx1a2b3c4d5e6f7g8h9",
        "name": "Classic T-Shirt",
        "sku": "TSHIRT-BLK-M",
        "images": [
          {}
        ]
      },
      "variant": {
        "id": "clx1a2b3c4d5e6f7g8h9",
        "name": "Black / M",
        "sku": "TSHIRT-BLK-M",
        "image": {
          "url": "string",
          "alt": "string"
        }
      },
      "modifiers": [
        {
          "modifierId": "clx1a2b3c4d5e6f7g8h9",
          "modifierGroupId": "clx1a2b3c4d5e6f7g8h9",
          "name": "Extra cheese",
          "priceDelta": "5.00",
          "freeApplied": true,
          "effectivePrice": "5.00",
          "positionInGroup": 0
        }
      ],
      "modifiersTotal": "5.00",
      "parentCartItemId": "clx1a2b3c4d5e6f7g8h9",
      "createdAt": "2019-08-24T14:15:22Z",
      "updatedAt": "2019-08-24T14:15:22Z"
    }
  ],
  "itemCount": 2,
  "hasPriceChanges": true,
  "hasUnavailableItems": true,
  "unavailableItemIds": [
    "string"
  ],
  "expiresAt": "2019-08-24T14:15:22Z",
  "createdAt": "2019-08-24T14:15:22Z",
  "updatedAt": "2019-08-24T14:15:22Z",
  "reservation": {
    "hasReservation": true,
    "expiresAt": "2019-08-24T14:15:22Z",
    "remainingSeconds": 540,
    "strategy": "ON_PAYMENT",
    "countdownMessage": "Your items are reserved for 9 minutes"
  },
  "recommendations": {
    "recommendations": [
      {
        "id": "string",
        "name": "string",
        "slug": "string",
        "basePrice": "string",
        "salePrice": "string",
        "images": [
          {
            "url": "string",
            "alt": "string"
          }
        ],
        "type": "SIMPLE",
        "inventory": {
          "total": 0,
          "available": 0,
          "trackingMode": "TRACKED",
          "inStock": true,
          "canPurchase": true
        },
        "relationType": "string",
        "targetVariantId": "string",
        "requiresVariantSelection": true,
        "pinnedVariant": {
          "id": "string",
          "name": "string",
          "attributes": {}
        },
        "variants": [
          {
            "id": "string",
            "name": "string",
            "attributes": {},
            "image": {
              "url": "string",
              "alt": "string"
            },
            "price": "string",
            "salePrice": "string"
          }
        ]
      }
    ]
  },
  "upgrades": {
    "upgrades": {}
  },
  "bundles": {
    "bundles": [
      {
        "id": "string",
        "name": "string",
        "description": "string",
        "triggerProductId": "string",
        "productIds": [
          "string"
        ],
        "offeredProducts": [
          {
            "id": "string",
            "name": "string",
            "slug": "string",
            "basePrice": "string",
            "salePrice": "string",
            "images": [
              {
                "url": "string",
                "alt": "string"
              }
            ],
            "type": "SIMPLE",
            "variantId": "string",
            "requiresVariantSelection": true,
            "pinnedVariant": {
              "id": "string",
              "name": "string",
              "attributes": {}
            },
            "variants": [
              {
                "id": "string",
                "name": "string",
                "attributes": {},
                "image": {
                  "url": "string",
                  "alt": "string"
                },
                "price": "string",
                "salePrice": "string"
              }
            ],
            "originalPrice": "string",
            "discountedPrice": "string"
          }
        ],
        "discountType": "PERCENTAGE",
        "discountValue": "string",
        "totalOriginalPrice": "string",
        "totalDiscountedPrice": "string"
      }
    ]
  }
}

{
  "statusCode": 400,
  "code": "VALIDATION_FAILED",
  "message": "name should not be empty, price must be a positive number",
  "timestamp": "2026-08-23T10:15:00.000Z",
  "path": "/api/v1/cart/{cartId}/items/{itemId}"
}

{
  "statusCode": 401,
  "code": "UNAUTHORIZED",
  "message": "Invalid or expired credential",
  "timestamp": "2026-08-23T10:15:00.000Z",
  "path": "/api/v1/cart/{cartId}/items/{itemId}"
}

{
  "statusCode": 403,
  "code": "INSUFFICIENT_SCOPE",
  "message": "API key does not have the required scope: products:write",
  "timestamp": "2026-08-23T10:15:00.000Z",
  "path": "/api/v1/cart/{cartId}/items/{itemId}"
}

{
  "statusCode": 404,
  "code": "RESOURCE_NOT_FOUND",
  "message": "Resource not found",
  "timestamp": "2026-08-23T10:15:00.000Z",
  "path": "/api/v1/cart/{cartId}/items/{itemId}"
}

{
  "statusCode": 429,
  "code": "RATE_LIMITED",
  "message": "Too many requests",
  "details": {
    "retryAfterSeconds": 12
  },
  "timestamp": "2026-08-23T10:15:00.000Z",
  "path": "/api/v1/store"
}

Add item to cart

Add item to cart. POST /v1/cart/{cartId}/items in the Brainerce API.

Remove item from cart

Remove item from cart. DELETE /v1/cart/{cartId}/items/{itemId} in the Brainerce API.