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

# Post Case Message

> Reply on a Zinc support case, with optional attachments. Reopens a closed case.

Reply on a support case. Like [Create Case](https://www.zinc.com/docs/v2/api-reference/cases/create-case.md), this is a multipart form:

```bash theme={null}
curl -X POST "https://api.zinc.com/cases/3f2c9a8e-1b4d-4e6f-9a7b-2c8d5e1f0a3b/messages" \
  -H "Authorization: Bearer <your_api_key>" \
  -F "body=Here's a photo of the shipping label." \
  -F "files=@label.jpg"
```

* **body**: your message, up to 5,000 characters. It can be empty if you attach at least one file.
* **files** (optional): up to 5 attachments, 25 MB each, as JPEG, PNG, WebP, HEIC or PDF.

The response is the whole case with your message added. See [Get Case](https://www.zinc.com/docs/v2/api-reference/cases/get-case.md).

## Status after a reply

A reply moves the case to `open`, which means it's back with Zinc support.

Replying on a `closed` case **reopens** it, and the thread gets a `Case reopened` line. That's allowed only inside the order's case window (see [When a case can be opened](https://www.zinc.com/docs/v2/api-reference/cases/create-case.md#when-a-case-can-be-opened)):

* Past the window, the reply fails with `400`, `code: "case_not_allowed"` and `details.reason: "window_closed"`. Nothing is posted.
* If another case on the same order has been opened since this one closed, the reply fails with `409`. An order can have only one open case, and `details.case_id` names the open one. Reply there instead.

## Other errors

| Status | `code` | Cause |
| - | - | - |
| `404` | `not_found` | No case with that ID, or it belongs to another team |
| `413` | | A file is over 25 MB |
| `415` | | A file isn't JPEG, PNG, WebP, HEIC or PDF |
| `422` | `validation_error` | No message and no files, a message over 5,000 characters, or more than 5 files |


## OpenAPI

````yaml versions/latest.json POST /cases/{case_id}/messages
openapi: 3.1.0
info:
  title: Zinc
  summary: >-
    Zinc lets you search, buy, and return items from top online retailers with a
    single API.
  description: >-
    Search, buy, and return items from top online retailers with a single API.
    Supports AI agent ordering via MPP (HTTP 402) — no account required.
    Supported retailers include 1-800-Flowers, Ace Hardware, Amazon, Amazon CA,
    Amazon DE, Amazon FR, Amazon MX, Amazon UK, Barnes & Noble, Best Buy, Chewy,
    Gap, and 18 more. Ships to the US and 6 other countries (CA, DE, FR, GB, IT,
    MX). The listed retailers are the ones Zinc verifies with daily test orders,
    not the limit of what Zinc can buy from: checkout is attempted at most
    online stores, including Shopify-hosted ones. To ask about a specific store
    before ordering, call GET /retailers/check?url=... — it answers whether Zinc
    will attempt that URL.
  version: '2026-10-16'
  x-logo:
    url: https://mintlify.s3.us-west-1.amazonaws.com/zinc/logo/light.png
  contact:
    name: Zinc API Support
    email: support@zinc.com
    url: https://zinc.com/docs
  x-guidance: >-
    Zinc lets AI agents buy products from online retailers via a single API. Use
    POST /agent/orders to place an order — no Zinc account needed, payment is
    handled via MPP (HTTP 402 flow). Provide a product URL from a supported
    retailer, a shipping address, and max_price in cents. The API charges
    max_price + $1 API fee upfront and refunds the difference on completion. To
    find products first, the /agent/* data endpoints (search, products/search,
    products/offers, products/details) are MPP-paid at $0.01 per call;
    /agent/search returns orderable URLs to feed straight into /agent/orders.
    GET /retailers lists supported retailers for free (no payment or account).
    Authenticated equivalents (orders, products, managed-accounts) require a
    Bearer token (API key prefixed zn_); those orders are paid from a prefunded
    wallet — GET /wallet/me returns the spendable balance and per-order fee, so
    check it before POST /orders to avoid a 402. Orders are strict by default:
    if the gift option can't be applied or any item can't be bought, the whole
    order fails. When the user wants whatever can be shipped, send fulfillment:
    {"gift": "best_effort", "items": "best_effort"} and read
    fulfillment.concessions on the order to see what was relaxed. max_price is
    never relaxed. Docs: https://zinc.com/docs Supported retailers include
    1-800-Flowers, Ace Hardware, Amazon, Amazon CA, Amazon DE, Amazon FR, Amazon
    MX, Amazon UK, Barnes & Noble, Best Buy, Chewy, Gap, and 18 more, shipping
    to the US and 6 other countries (CA, DE, FR, GB, IT, MX). The listed
    retailers are the ones Zinc verifies with daily test orders, not the limit
    of what Zinc can buy from: checkout is attempted at most online stores,
    including Shopify-hosted ones. To ask about a specific store before
    ordering, call GET /retailers/check?url=... — it answers whether Zinc will
    attempt that URL.
  x-supported-retailers:
    - 1-800-Flowers
    - Ace Hardware
    - Amazon
    - Amazon CA
    - Amazon DE
    - Amazon FR
    - Amazon MX
    - Amazon UK
    - Barnes & Noble
    - Best Buy
    - Chewy
    - Gap
    - Grainger
    - IBS
    - Lowe's
    - Macys
    - McMaster-Carr
    - Partstown
    - Pokémon Center
    - Sephora
    - Target
    - The Home Depot
    - TikTok
    - Uniqlo
    - Walmart
    - Wayfair
    - Zinc
    - eBay
    - libraccio
    - zazzle
  x-supported-countries:
    - US
    - CA
    - DE
    - FR
    - GB
    - IT
    - MX
servers:
  - url: https://api.zinc.com
    description: Production
security:
  - BearerAuth: []
paths:
  /cases/{case_id}/messages:
    post:
      tags:
        - cases
      summary: Post Case Message
      description: |-
        Reply on a case. Multipart form: `body` and up to 5 `files`.

        Replying on a closed case reopens it, within the case window.
      operationId: post_case_message_cases__case_id__messages_post
      parameters:
        - name: case_id
          in: path
          required: true
          schema:
            type: string
            format: uuid
            title: Case Id
        - name: authorization
          in: header
          required: false
          schema:
            anyOf:
              - type: string
              - type: 'null'
            title: Authorization
      requestBody:
        content:
          multipart/form-data:
            schema:
              $ref: >-
                #/components/schemas/Body_post_case_message_cases__case_id__messages_post
      responses:
        '201':
          description: Successful Response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CaseResponse'
        '400':
          description: The case is closed and past the window for reopening
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '409':
          description: >-
            Replying would reopen this closed case, but another case on the
            order is already open
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '422':
          description: Validation Error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/HTTPValidationError'
components:
  schemas:
    Body_post_case_message_cases__case_id__messages_post:
      properties:
        body:
          type: string
          title: Body
          default: ''
        files:
          items:
            type: string
            format: binary
          type: array
          title: Files
          default: []
      type: object
      title: Body_post_case_message_cases__case_id__messages_post
    CaseResponse:
      properties:
        id:
          type: string
          format: uuid
          title: Id
        order_id:
          type: string
          format: uuid
          title: Order Id
        return_request_id:
          anyOf:
            - type: string
              format: uuid
            - type: 'null'
          title: Return Request Id
        reason:
          $ref: '#/components/schemas/CaseReason'
        status:
          $ref: '#/components/schemas/CaseStatus'
          description: >-
            `open` — waiting on Zinc. `waiting_on_customer` — Zinc replied and
            is waiting on you. `on_hold` — waiting on the retailer or carrier.
            `closed` — resolved; replying reopens it within the case window.
        credited_amount:
          type: integer
          title: Credited Amount
          description: >-
            Total wallet credit issued from this case, in cents (net of
            reversals).
          default: 0
        opened_by_name:
          anyOf:
            - type: string
            - type: 'null'
          title: Opened By Name
          description: >-
            Who opened the case: a teammate's name, or `Zinc support` when Zinc
            reached out. (The `case.created` webhook's `opened_by` is the side
            instead: `customer` or `zinc`.)
        created_at:
          type: string
          format: date-time
          title: Created At
        updated_at:
          type: string
          format: date-time
          title: Updated At
        closed_at:
          anyOf:
            - type: string
              format: date-time
            - type: 'null'
          title: Closed At
        messages:
          items:
            $ref: '#/components/schemas/CaseMessageResponse'
          type: array
          title: Messages
          default: []
      type: object
      required:
        - id
        - order_id
        - reason
        - status
        - created_at
        - updated_at
      title: CaseResponse
    ErrorResponse:
      properties:
        error:
          $ref: '#/components/schemas/ErrorDetail'
      type: object
      required:
        - error
      title: ErrorResponse
      description: Wrapper for error responses.
    HTTPValidationError:
      properties:
        detail:
          items:
            $ref: '#/components/schemas/ValidationError'
          type: array
          title: Detail
      type: object
      title: HTTPValidationError
    CaseReason:
      type: string
      enum:
        - not_received
        - missing_item
        - late
        - damaged_or_wrong_item
        - cancellation
        - address_change
        - return
        - billing
        - other
      title: CaseReason
      description: |-
        What a support case is about. Routing and reporting only — no reason
        triggers automation.
    CaseStatus:
      type: string
      enum:
        - open
        - waiting_on_customer
        - on_hold
        - closed
      title: CaseStatus
      description: >-
        Whose move it is on a support case.


        Only ``closed`` is terminal, and not even that for long: a customer
        reply

        inside the open window reopens a closed case rather than starting a new
        one.
    CaseMessageResponse:
      properties:
        id:
          type: string
          format: uuid
          title: Id
        author:
          type: string
          enum:
            - customer
            - zinc
            - system
          title: Author
          description: >-
            `customer` (you or a teammate), `zinc` (our support team), or
            `system` (status changes, reopens, credits).
        author_name:
          anyOf:
            - type: string
            - type: 'null'
          title: Author Name
          description: >-
            Who wrote it: the teammate's name for `customer` messages, `Zinc
            support` for `zinc`, null for `system` lines.
        from_you:
          type: boolean
          title: From You
          description: True when the caller wrote this message.
          default: false
        body:
          type: string
          title: Body
        attachments:
          items:
            $ref: '#/components/schemas/CaseAttachment'
          type: array
          title: Attachments
          default: []
        created_at:
          type: string
          format: date-time
          title: Created At
      type: object
      required:
        - id
        - author
        - body
        - created_at
      title: CaseMessageResponse
    ErrorDetail:
      properties:
        code:
          $ref: '#/components/schemas/ErrorCode'
        message:
          type: string
          title: Message
        details:
          anyOf:
            - additionalProperties: true
              type: object
            - type: 'null'
          title: Details
      type: object
      required:
        - code
        - message
      title: ErrorDetail
      description: Standard error response body.
    ValidationError:
      properties:
        loc:
          items:
            anyOf:
              - type: string
              - type: integer
          type: array
          title: Location
        msg:
          type: string
          title: Message
        type:
          type: string
          title: Error Type
      type: object
      required:
        - loc
        - msg
        - type
      title: ValidationError
    CaseAttachment:
      properties:
        id:
          type: string
          format: uuid
          title: Id
        filename:
          type: string
          title: Filename
        content_type:
          type: string
          title: Content Type
        size_bytes:
          type: integer
          title: Size Bytes
        url:
          anyOf:
            - type: string
            - type: 'null'
          title: Url
          description: >-
            Presigned download URL, valid for 7 days from the response. Re-fetch
            the case for a fresh one.
      type: object
      required:
        - id
        - filename
        - content_type
        - size_bytes
      title: CaseAttachment
    ErrorCode:
      type: string
      enum:
        - unauthorized
        - forbidden
        - invalid_token
        - token_expired
        - not_found
        - already_exists
        - validation_error
        - insufficient_funds
        - authorization_pending
        - slow_down
        - expired_token
        - access_denied
        - payment_failed
        - payment_method_required
        - payment_required
        - invalid_payment_method
        - invalid_shipping_address
        - url_unreachable
        - non_us_retailer
        - unsupported_retailer
        - unsupported_country
        - retailer_country_not_supported
        - guest_checkout_not_supported
        - invalid_variant
        - out_of_stock
        - shipping_unavailable
        - order_not_cancellable
        - return_not_allowed
        - case_not_allowed
        - external_service_error
        - stripe_error
        - stytch_error
        - internal_error
        - bad_request
        - rate_limit_exceeded
        - service_unavailable
      title: ErrorCode
      description: Standardized error codes for the API.
  securitySchemes:
    BearerAuth:
      type: apiKey
      in: header
      name: Authorization
      description: Zinc API key (Bearer zn_...)

````

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