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

# Call a merchant agent using A2A

> Official A2A 1.0 JSON-RPC SendMessage, GetTask and CancelTask.

### Authentication

Uses the existing customer JWT from /api/embed/{deploymentId}/session; send the same Origin when creating and using the session.

### Messages

SendMessage accepts text user messages with a UUID messageId and up to 4000 characters. For asynchronous execution set configuration.returnImmediately=true and retrieve the task. Every task is bound to the customer session.

Bot verification and storefront protection apply. Payment proofs belong in the checkout completion endpoint, outside model messages.

### Signed offers and buyer agents

Payable offers in purchase-offers artifacts include checkoutJwt when the platform signing key is configured. Requests may carry a Web Bot Auth signature; the verified agent origin is recorded on resulting offers and orders.



## OpenAPI

````yaml /openapi.json post /api/embed/{deploymentId}/a2a
openapi: 3.1.0
info:
  title: OmniCommerce API
  version: 1.0.0
  license:
    name: Proprietary
    url: https://omnicommerce.sg/terms
  description: >-
    OmniCommerce API surface for agents and developer integrations. Includes
    public endpoints (merchant discovery, product search, compare, catalog, ACO
    retrieval) and authenticated endpoints (product management via API key
    Bearer tokens).
servers:
  - url: https://omnicommerce.sg
    description: Production
  - url: http://localhost:3000
    description: Local development
security: []
tags:
  - name: agentic-checkout
    description: Merchant-fulfilled agentic checkout
    x-group: Agentic Checkout
  - name: agents
    description: agents
    x-group: Agents
  - name: analytics
    description: Sales performance across marketplaces
    x-group: Analytics
  - name: aops
    description: Agent operating procedures
    x-group: AOPs
  - name: branding
    description: branding
    x-group: Branding
  - name: campaigns
    description: Campaign briefs, offer windows, and marketplace runs
    x-group: Campaigns
  - name: developer-platform
    description: Authenticated developer platform APIs
    x-group: Developer Platform
  - name: documents
    description: Knowledge base document uploads
    x-group: Knowledge Base
  - name: inventory
    description: Inventory quantities, planning signals, and marketplace listing absence
    x-group: Inventory
  - name: looks
    description: AI-styled product looks
    x-group: Looks
  - name: oauth
    description: OAuth token endpoints
    x-group: OAuth
  - name: orders
    description: Workspace and agentic orders
    x-group: Orders
  - name: organizations
    description: Organization management
    x-group: Organizations
  - name: price-books
    description: Marketplace list-price markup rules
    x-group: Price Books
  - name: products
    description: Product CRUD, bulk import, enrichment, publish, and delist
    x-group: Products
  - name: promotions
    description: Central promotions and marketplace sync
    x-group: Promotions
  - name: public-agent
    description: Public agent discovery and catalog APIs
    x-group: Public Agent
  - name: returns
    description: returns
    x-group: Returns
  - name: reviews
    description: Marketplace product reviews and seller replies
    x-group: Reviews
  - name: settlements
    description: settlements
    x-group: Settlements
  - name: ucp
    description: Universal Commerce Protocol
    x-group: UCP
paths:
  /api/embed/{deploymentId}/a2a:
    post:
      tags:
        - agentic-checkout
      summary: Call a merchant agent using A2A
      description: >-
        Official A2A 1.0 JSON-RPC SendMessage, GetTask and CancelTask.


        ### Authentication


        Uses the existing customer JWT from /api/embed/{deploymentId}/session;
        send the same Origin when creating and using the session.


        ### Messages


        SendMessage accepts text user messages with a UUID messageId and up to
        4000 characters. For asynchronous execution set
        configuration.returnImmediately=true and retrieve the task. Every task
        is bound to the customer session.


        Bot verification and storefront protection apply. Payment proofs belong
        in the checkout completion endpoint, outside model messages.


        ### Signed offers and buyer agents


        Payable offers in purchase-offers artifacts include checkoutJwt when the
        platform signing key is configured. Requests may carry a Web Bot Auth
        signature; the verified agent origin is recorded on resulting offers and
        orders.
      operationId: post_embed_by_deploymentid_a2a
      parameters:
        - name: deploymentId
          in: path
          required: true
          schema:
            type: string
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              description: A2A 1.0 JSON-RPC envelope, validated by @a2a-js/sdk.
      responses:
        '200':
          description: A2A JSON-RPC task or protocol error.
        '401':
          description: Invalid customer session or buyer-agent signature.
        '403':
          description: Deployment or origin mismatch.
        '429':
          description: Storefront protection limit.
      security:
        - customerSession: []
components:
  securitySchemes:
    customerSession:
      type: http
      scheme: bearer
      bearerFormat: JWT
      description: >-
        Customer session from /api/embed/{deploymentId}/session. Origin and
        deployment scope must match.

````

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