> ## 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. # Complete UCP Checkout Session > Settle the selected rail and create a native `agentic` order. Settlement failures return HTTP 402 with the checkout still ready for payment. Requires `UCP-Agent` and OAuth `checkout:write`. ## OpenAPI ````yaml /openapi.json post /ucp/v1/checkout-sessions/{sessionId}/complete 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/{sessionId}/complete: post: tags: - ucp summary: Complete UCP Checkout Session description: >- Settle the selected rail and create a native `agentic` order. Settlement failures return HTTP 402 with the checkout still ready for payment. Requires `UCP-Agent` and OAuth `checkout:write`. operationId: post_ucp_v1_checkout_sessions_by_sessionid_complete parameters: - name: sessionId in: path required: true schema: type: string - name: UCP-Agent in: header required: true description: UCP agent identity, for example `agent.example/1.0`. schema: type: string maxLength: 240 - name: organizationId in: query required: false description: >- Optional organization scope for session-authenticated calls. OAuth client credentials resolve the organization from the token. schema: type: string maxLength: 120 - 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 properties: idempotency_key: type: string maxLength: 180 paymentProof: type: object additionalProperties: true payment: type: object additionalProperties: true responses: '200': description: Checkout completed and native order 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 '401': description: Unauthorized '402': description: Settlement failed; the checkout remains ready for payment. 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 '403': description: Forbidden or checkout not enabled '404': description: Checkout session not found '409': description: Terminal or expired checkout session '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. ````