Cart
What it does: Manages what the customer has selected — items, quantities, rewards, and promos — before they proceed to checkout.
Why it matters: Cart integrity is critical to revenue. Pricing errors in the cart, lost cart state, or failed promo applications directly cause abandoned orders.
Feature Table
| Feature | Problem It Solves | What It Does | How It Works | Dependencies | Prerequisites | Limitations | Impacted Metrics |
|---|---|---|---|---|---|---|---|
| Add Item to Cart | Customer wants to start an order | Adds a menu item (with chosen modifiers) to the cart | Byte Helium sends add-line request to Cart Service; price is calculated by backend at add time | Cart Service, Menu Service | Localisation and order mode set | Cart tied to session; guest carts lost if session expires | Add-to-cart rate |
| Update / Remove Cart Line | Customer changes their mind | Updates quantity or removes an item from the cart | Cart Service update/remove line call; totals recalculated | Cart Service | Item must be in cart | Real-time repricing may surface price changes | Cart modification rate |
| Apply Promo Code | Customer has a promo code | Validates and attaches a promo code to the cart for a discount | Byte Helium sends promo code to Cart/Promo service; eligibility validated server-side; cart repriced | Cart Service, Promo Engine | Cart must have items; promo must be valid for market | Invalid code returns error (400) but keeps cart intact; one promo code at a time (market config) | Promo redemption rate, discount rate |
| Add Reward to Cart | Loyalty member wants to use a reward | Attaches a loyalty reward to the cart (e.g., free item) | Reward validated with Loyalty service; reward token attached to cart | Loyalty service, Cart Service | Customer must be signed in and enrolled in Loyalty | Reward must not be expired; only one reward type per cart (market config) | Reward attach rate |
| Remove Reward from Cart | Customer changes their mind about a reward | Detaches the reward from the cart | Loyalty service reward removed; cart totals updated | Loyalty service, Cart Service | Reward must be in cart | Reward returns to available balance | Cart modification rate |
Technical Sources
📎 Technical Source: Add Item to Cart / Apply Promo
- FRD References: FRD-HEL-011, FRD-HEL-048
- TRD Domain: Cart
- Key Interfaces / APIs: Add/Update/Remove Line (App → Cart), Apply/Remove Promo (App → Cart)
- Data Contracts: Cart (id, lines[], totals, benefits[]) — idempotent ops
- Source Summary:
- All cart operations are idempotent (safe to retry)
- Pricing correctness: 100% accuracy required (enforced via golden tests in backend)
- Invalid promo (400): error shown, cart state preserved
- Cart API: additive changes only, 90-day deprecation window
- Promo eligibility is always server-side — never computed in Byte Helium
See it in the wiki
- How customers experience the cart front-end → Order and Get: Cart
- How to create and manage promotions → Admin Portal Guide: Promotions and Promotion Recipes