Fix Magento API Issues for Integration

Task Brief: Fix Magento API Issues for Flutter Mobile App Integration

We need a backend Magento developer to fix two critical issues in our Magento API used by a live Flutter mobile app. The mobile app is already integrated — these are isolated issues on the API side.

You will work against a testable API and Git-connected frontend team. All integration and testing support is provided.


Issue 1: Incorrect Segmentation Key in Category Response

- The Magento API returns product segmentation key as `Shop` instead of the correct product `category` in 4 specific product cases.
- This breaks face visualisation mapping in the app
- Other categories work fine, so the issue is with inconsistent key assignment or filtering.

Expected:
```json
[{ "category": "#421927", "visibility": 2 }]
```

Current broken response:
```json
[{ "Shop": "#421927", "visibility": 2 }]
```

Issue 2: GiftCard/Promo Code API Returns Empty Response

- When submitting a valid promo/gift card code (e.g. `cha06061234567`) with a populated cart and valid bearer token, the API responds:
```
GiftCard API Response is :: []
```
- This occurs even when the code is active and has valid date range and amount.
- We suspect the API is failing to detect the code properly or session/cart linkage is broken.

Expected:
- API should return the remaining balance or validation details, not `::[]`.

Provided:
- Full Magento API source access
- Confirmed working setup for authentication and token flow
- API test logs and screenshots


Deadline:
Fixes should be implemented and testable within 2–3 days. I will guide you down to code level so I know where it is even.

Please note: you are hired to deliver, not to come up with excuses and bloat timeline. The system is more than 4 years old so it is well analysed and in production.