> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fluid.app/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> For new direct REST integrations, use the v2026-04 surfaces. The @fluid-app FairShare SDK continues to use its own published public-v2025-06 contract.
> Authenticate with the header Authorization: Bearer <token>; public storefront read endpoints require no auth.
> Lists use cursor pagination via the page[cursor] and page[limit] query params; follow meta.pagination.next_cursor until it is null.
> Never use /api/company/v1 or /api/v1 paths, page/per_page params, or offset pagination — they are legacy.
> The OpenAPI specs under api-reference/ are the authoritative contracts; prefer them over prose when in doubt. api-reference/storefront-v2026-04.yaml covers the v2026-04 storefront surface (/api/v202604/... paths); api-reference/auth-v0.yaml covers the unversioned auth surface (/api/... paths — authentication, MFA, social auth, and token exchange); api-reference/checkout-v2026-04.yaml covers the v2026-04 checkout surface (/api/checkout/v2026-04/... paths — carts, cart auth, discounts, items, subscriptions, orders, enrollments, and store config); api-reference/public-v2025-06.yaml covers the Public SDK surface used by the @fluid-app FairShare SDK, including its parallel cart lifecycle, browser integrations, versioned payment callbacks, unversioned public utilities, and the cart price-override operation; api-reference/payment-v2026-04.yaml covers the v2026-04 payment gateway admin surface (/api/payment/v2026-04/... paths, bearer-authenticated — gateway CRUD, gateway purchase/authorize/$0-verify, transaction list/show and capture/void/credit, and merchant payment configuration); api-reference/payments-v2026-04.yaml covers the v2026-04 cart payment surface (/api/payments/v2026-04/carts/{cart_token}/... paths, authenticated by the cart token in the path with no bearer — payment-method selection, VGS card tokenization, 3D Secure verification, and PayPal/Braintree/Klarna/Apple Pay flows); api-reference/commerce-v2026-04.yaml covers the v2026-04 commerce order-editing surface (/api/v202604/orders/{order_id}/edits paths, bearer-authenticated — post-checkout order edits that atomically insert items and add adjustments/discounts, with an optional dry-run preview); api-reference/webhooks-v0.yaml covers the unversioned webhooks surface (/api/... paths — webhook registration, delivery payloads, callback registrations, company events, and webhook/callback schemas).
> Successful responses wrap the resource payload alongside a top-level integer status and a meta object.

# Work with the category hierarchy

> Create child categories, list top-level categories, and traverse parents and children using parent_id and has_children.

Categories can be nested into a tree: a category may have a parent and any number of children. This guide covers creating child categories, listing the top level, and walking the tree.

<Note>
  Hierarchy is a **category-only** feature. Collections have no parent/child relationship — their responses carry no `parent_id`, `has_children`, or `position`, and their write bodies accept no `parent_id`. Everything in this guide applies to categories only.
</Note>

## The fields that model the tree

Three fields on a category describe its place in the tree:

<ResponseField name="parent_id" type="integer | null">
  The id of the parent category, or `null` when the category is at the root (top level).
</ResponseField>

<ResponseField name="has_children" type="boolean">
  `true` when the category has at least one child. Use it to decide whether to fetch a level deeper.
</ResponseField>

<ResponseField name="position" type="integer">
  The category's order among its siblings. The default sort (`position` then `id`) uses it.
</ResponseField>

## Create a child category

To nest a category under another, set `parent_id` to the parent's id when you create it. Leaving `parent_id` out (or `null`) creates a top-level category.

```bash theme={null}
curl -X POST "https://api.fluid.app/api/v202604/company/categories" \
  -H "Authorization: Bearer <your_token>" \
  -H "Content-Type: application/json" \
  -d '{
    "category": {
      "title": "Clearance",
      "parent_id": 4821,
      "position": 1
    }
  }'
```

You can also move an existing category by patching its `parent_id`. Set it to another id to re-parent, or to `null` to promote it to the top level:

```bash theme={null}
curl -X PATCH "https://api.fluid.app/api/v202604/company/categories/4822" \
  -H "Authorization: Bearer <your_token>" \
  -H "Content-Type: application/json" \
  -d '{
    "category": {
      "parent_id": null
    }
  }'
```

Use `position` to order siblings within a level.

## List top-level categories

The public catalog's `filter[parent_id]` selects a single level of the tree. Pass the literal string `"root"` to get only top-level categories:

```bash theme={null}
curl "https://acme.fluid.app/api/v202604/categories?filter[parent_id]=root"
```

## List the children of a category

Pass a category id (as a string) to `filter[parent_id]` to get that category's direct children:

```bash theme={null}
curl "https://acme.fluid.app/api/v202604/categories?filter[parent_id]=4821"
```

Each returned child carries its own `has_children`, so you know whether it has a further level beneath it.

## Traverse the tree

Combine `filter[parent_id]` with `has_children` to walk down the tree one level at a time:

<Steps>
  <Step title="Start at the root">
    Fetch the top level with `filter[parent_id]=root`.

    ```bash theme={null}
    curl "https://acme.fluid.app/api/v202604/categories?filter[parent_id]=root"
    ```
  </Step>

  <Step title="Descend into categories that have children">
    For each returned category where `has_children` is `true`, fetch its children with `filter[parent_id]=<id>`.

    ```bash theme={null}
    curl "https://acme.fluid.app/api/v202604/categories?filter[parent_id]=4821"
    ```
  </Step>

  <Step title="Repeat until has_children is false">
    Keep descending into any child whose `has_children` is `true`. A category with `has_children: false` is a leaf.
  </Step>
</Steps>

To walk **up** the tree instead, read a category's `parent_id` and fetch that parent by id with the company show endpoint `GET /api/v202604/company/categories/{id}`. The public show endpoint resolves by slug rather than id, so on the public surface you locate the parent among catalog results (each row carries both `id` and `slug`) and then fetch it with `GET /api/v202604/categories/{slug}`.

<Note>
  `filter[parent_id]` is accepted on **both** the public catalog and the company index (`GET /api/v202604/company/categories`) — the two surfaces share one query contract. They differ only in scope: the public catalog returns only live categories, while the company index returns every lifecycle state (draft, scheduled, and archived included). So to build the full tree as an admin you can either filter the company index by `filter[parent_id]`, or page through it unfiltered and group the rows client-side by their `parent_id` field, which is present on every row.
</Note>

## Next steps

* [Find and create categories and collections](/api/guides/find-and-create-categories-and-collections) — the full create and lookup surface.
* [Control country availability](/api/guides/country-availability) — combine hierarchy with per-country visibility.