Affirm Authorization API

openapi: 3.1.0
info:
  title: Affirm Checkout Authorization API
  description: The Affirm Checkout API enables merchants to initiate and manage the Affirm buy now pay later checkout flow for customers at the point of purchase. It provides endpoints to create and store checkout sessions, read and update checkout objects, and resend checkout links via email or SMS. The API supports both redirect and direct checkout integration patterns. Once a customer authorizes a loan, the resulting checkout token is exchanged server-side to complete the transaction authorization via the Transactions API. Authentication uses HTTP Basic Authentication with the merchant's public and private API keys.
  version: '1.0'
  contact:
    name: Affirm Developer Support
    url: https://docs.affirm.com/developers/docs/development-quickstart
  termsOfService: https://www.affirm.com/legal/merchant-terms
servers:
- url: https://api.affirm.com/api/v1
  description: Production Server
- url: https://sandbox.affirm.com/api/v1
  description: Sandbox Server
security:
- basicAuth: []
tags:
- name: Authorization
  description: Server-side operations for authorizing Affirm transactions after a customer completes the checkout flow and a checkout token is returned.
paths:
  /transactions:
    post:
      operationId: authorizeDirectTransaction
      summary: Affirm Authorize a Transaction
      description: Exchanges a checkout token for a transaction authorization, completing the server-side portion of the Direct API flow. This call must be made from the merchant server after the browser-side affirm.js returns a checkout token via the user_confirmation_url callback. The authorization places a hold on the customer's Affirm credit. The resulting transaction must be captured within the authorization window to transfer funds to the merchant.
      tags:
      - Authorization
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
              - checkout_token
              properties:
                checkout_token:
                  type: string
                  description: The checkout token returned by the Affirm checkout flow via the user_confirmation_url callback. This token is single-use and expires after a short window.
                order_id:
                  type: string
                  description: The merchant's internal order identifier to associate with this authorization for reconciliation purposes.
            examples:
              authorizeDirectTransactionRequestExample:
                summary: Default authorizeDirectTransaction request
                x-microcks-default: true
                value:
                  checkout_token: abc123def456abc123def456abc123de
                  order_id: '500123'
      responses:
        '200':
          description: Transaction authorized successfully.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Transaction'
              examples:
                authorizeDirectTransaction200Example:
                  summary: Default authorizeDirectTransaction 200 response
                  x-microcks-default: true
                  value:
                    id: '500123'
                    checkout_id: '500123'
                    order_id: '500123'
                    status: authorized
                    amount: 1
                    amount_refunded: 1
                    currency: USD
                    created: '2025-03-15T14:30:00Z'
                    authorization_expiration: '2025-03-15T14:30:00Z'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
      x-microcks-operation:
        delay: 0
        dispatcher: FALLBACK
  /files:
    post:
      operationId: uploadFile
      summary: Affirm Upload a File
      description: Uploads a file to Affirm's servers for use as dispute evidence. Returns a file identifier that can be referenced when submitting evidence via the Disputes API. Supported file types include images (JPEG, PNG) and documents (PDF).
      tags:
      - Authorization
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              required:
              - file
              properties:
                file:
                  type: string
                  format: binary
                  description: The file to upload as binary data.
                purpose:
                  type: string
                  description: The intended purpose of the uploaded file.
                  enum:
                  - dispute_evidence
      responses:
        '200':
          description: File uploaded successfully.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/FileObject'
              examples:
                uploadFile200Example:
                  summary: Default uploadFile 200 response
                  x-microcks-default: true
                  value:
                    id: '500123'
                    filename: Example Merchant
                    size: 1
                    content_type: standard
                    purpose: example_value
                    created: '2025-03-15T14:30:00Z'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthorized'
      x-microcks-operation:
        delay: 0
        dispatcher: FALLBACK
  /files/{id}:
    get:
      operationId: downloadFile
      summary: Affirm Download a File
      description: Downloads a previously uploaded file by its identifier. Returns the raw file content with the appropriate content type header.
      tags:
      - Authorization
      parameters:
      - name: id
        in: path
        required: true
        description: The unique identifier of the file to download.
        schema:
          type: string
        example: '500123'
      responses:
        '200':
          description: File content returned successfully.
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary
        '401':
          $ref: '#/components/responses/Unauthorized'
        '404':
          $ref: '#/components/responses/NotFound'
      x-microcks-operation:
        delay: 0
        dispatcher: FALLBACK
components:
  responses:
    Unauthorized:
      description: Unauthorized. Authentication credentials are missing or invalid.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    BadRequest:
      description: Bad request. The request body or parameters are invalid.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    NotFound:
      description: Not found. The requested resource does not exist.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  schemas:
    Transaction:
      type: object
      description: Represents an Affirm payment transaction at any point in its lifecycle.
      properties:
        id:
          type: string
          description: Unique identifier for this transaction.
          example: '500123'
        checkout_id:
          type: string
          description: Identifier of the checkout session that originated this transaction.
          example: '500123'
        order_id:
          type: string
          description: Merchant's internal order identifier.
          example: '500123'
        status:
          type: string
          description: Current lifecycle status of the transaction.
          enum:
          - authorized
          - captured
          - voided
          - refunded
          - partially_refunded
          example: authorized
        amount:
          type: integer
          description: Original authorized amount in cents.
          example: 1
        amount_refunded:
          type: integer
          description: Cumulative amount refunded in cents.
          example: 1
        currency:
          type: string
          description: ISO 4217 currency code.
          example: USD
        created:
          type: string
          format: date-time
          description: Creation timestamp in RFC 3339 format.
          example: '2025-03-15T14:30:00Z'
        authorization_expiration:
          type: string
          format: date-time
          description: Timestamp after which the authorization can no longer be captured.
          example: '2025-03-15T14:30:00Z'
    FileObject:
      type: object
      description: Represents a file uploaded to Affirm's servers.
      properties:
        id:
          type: string
          description: Unique identifier for the uploaded file.
          example: '500123'
        filename:
          type: string
          description: Original filename of the uploaded file.
          example: Example Merchant
        size:
          type: integer
          description: File size in bytes.
          example: 1
        content_type:
          type: string
          description: MIME type of the uploaded file.
          example: standard
        purpose:
          type: string
          description: Intended purpose of the file.
          example: example_value
        created:
          type: string
          format: date-time
          description: Upload timestamp in RFC 3339 format.
          example: '2025-03-15T14:30:00Z'
    Error:
      type: object
      description: Standard error response returned by the Affirm API.
      properties:
        status_code:
          type: integer
          description: HTTP status code of the error.
          example: 1
        code:
          type: string
          description: Machine-readable error code string.
          example: example_value
        message:
          type: string
          description: Human-readable description of the error.
          example: example_value
  securitySchemes:
    basicAuth:
      type: http
      scheme: basic
      description: HTTP Basic Authentication using the merchant's public API key as the username and private API key as the password, Base64-encoded as per RFC 7617.
externalDocs:
  description: Affirm Checkout API Reference
  url: https://docs.affirm.com/developers/reference/the-checkout-object