> ## Documentation Index > Fetch the complete documentation index at: https://docs.omnicommerce.sg/llms.txt > Use this file to discover all available pages before exploring further. # Create UCP Checkout Session > Create a UCP shopping checkout session against the authenticated organization. The facade translates UCP line items to native agentic checkout sessions, reserves inventory, and returns a UCP checkout resource. Requires `UCP-Agent` and OAuth `checkout:write`. ## OpenAPI ````yaml /openapi.json post /ucp/v1/checkout-sessions 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: commerce description: Root commerce discovery x-group: Commerce - name: developer-platform description: Authenticated developer platform APIs x-group: Developer Platform - 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, and publish 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: settlements description: settlements x-group: Settlements - name: ucp description: Universal Commerce Protocol x-group: UCP paths: /ucp/v1/checkout-sessions: post: tags: - ucp summary: Create UCP Checkout Session description: >- Create a UCP shopping checkout session against the authenticated organization. The facade translates UCP line items to native agentic checkout sessions, reserves inventory, and returns a UCP checkout resource. Requires `UCP-Agent` and OAuth `checkout:write`. operationId: post_ucp_v1_checkout_sessions parameters: - name: UCP-Agent in: header required: true description: UCP agent identity, for example `agent.example/1.0`. schema: type: string maxLength: 240 - name: Idempotency-Key in: header required: false description: Optional idempotency key for safe retries. schema: type: string maxLength: 180 requestBody: required: true content: application/json: schema: type: object additionalProperties: true required: - line_items properties: line_items: type: array minItems: 1 maxItems: 100 items: type: object additionalProperties: true required: - item - quantity properties: item: type: object additionalProperties: true required: - id properties: id: type: string description: OmniCommerce product UUID. maxLength: 160 title: type: string price: type: integer image_url: type: string quantity: type: integer minimum: 1 maximum: 999 buyer: type: object additionalProperties: true fulfillment: type: object additionalProperties: true payment: type: object additionalProperties: true payment_rail: type: string enum: - acp_stripe - x402 default: acp_stripe metadata: type: object additionalProperties: true example: line_items: - item: id: 00000000-0000-4000-8000-000000000001 quantity: 1 buyer: email: buyer@example.com payment_rail: acp_stripe responses: '201': description: UCP checkout session created. content: application/json: schema: type: object additionalProperties: true required: - ucp - id - line_items - status - currency - totals properties: ucp: type: object additionalProperties: true id: type: string line_items: type: array items: type: object additionalProperties: true required: - item - quantity properties: item: type: object additionalProperties: true required: - id properties: id: type: string description: OmniCommerce product UUID. maxLength: 160 title: type: string price: type: integer image_url: type: string quantity: type: integer minimum: 1 maximum: 999 buyer: type: object additionalProperties: true fulfillment: type: object additionalProperties: true status: type: string enum: - ready_for_complete - completed - canceled currency: type: string totals: type: array items: type: object additionalProperties: true payment: type: object additionalProperties: true order: type: object additionalProperties: true settlement: type: object additionalProperties: true '400': description: Bad Request content: application/json: schema: type: object additionalProperties: true properties: ucp: type: object additionalProperties: true messages: type: array items: type: object additionalProperties: true '401': description: Unauthorized '403': description: Forbidden or checkout not enabled '409': description: Insufficient inventory '500': description: Internal Server Error security: - bearerAuth: [] components: securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: API Key description: >- Bearer API key for server-to-server access. Session auth is also supported in first-party UI flows. ````