Billie

Billie Authentication API

This API uses OAuth 2.0 for secure authentication. Different keys are used for the `sandbox` and `production` environments. Both systems operate completely independent, however both show largely the same response behaviour. The major difference is that sandbox does not trigger any payment events (payout to merchant, repayment by debtors, etc.). To obtain your credentials for both environments please contact Billie's merchant integration support via telephone ( [+49-30-120872485](tel:+4930120872485) ) or email ( pad@billie.io ). This authentication mechanism is based on the OAuth 2.0 protocol and requires a Client ID and a Client Secret Key (client credentials). Before triggering any API call, a so called JSON web token (JWT) must be requested through the `oauth/token` endpoint described below by using your client credentials. In all following requests / API calls, this JWT token is used for authorization and must be passed as type "Bearer" token in the Authorization header. Example: `Authorization: Bearer eyJhbGciOiJIUzI...` Renewal of the bearer token / JWT: Every token expires automatically after 8 hours. After expiration of an existing token a new token must be requested through the `POST oauth/token` endpoint. Implementation best practice is to always try sending API calls first with the previously stored token. Sending API calls with an expired token will be answered with an `HTTP 401` (Unauthorized request or invalid credentials) response. After receiving the `401` error you will simply need to request a new token by triggering again the `oauth/token` endpoint. After receiving the new valid token, resend the previously failed API call. This procedure allows for optimal API interaction, ensures reduced system load on both ends, and is easy to implement as you don't need to keep track of token expiration times. There is another endpoint available for checking if a token is still valid or not: `GET oauth/token`.

Documentation GitHub OpenAPI

Operations 3

GET /oauth/authorization Validate OAuth Token #

POST /oauth/token Request OAuth Token #

POST /oauth/token/revoke Revoke OAuth Token #

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OpenAPI Specification

openapi: 3.2.0
info:
  title: Billie Direct Authentication API
  description: '# Introduction


    With PayAfterDelivery (PAD) / "Rechnungskauf" Billie offers a convenient, secure and simple way to allow your

    B2B-customers to pay on invoice.'
  termsOfService: https://www.billie.io/agb/
  license:
    name: © Billie GmbH, 2020
    url: https://www.billie.io/agb/
  version: v2025.11
  x-logo:
    url: data:image/svg+xml;base64,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
    href: '#'
servers:
- url: https://paella-sandbox.billie.io/api/v2
  description: Test Sandbox API
- url: https://paella.billie.io/api/v2
  description: Production API
tags:
- name: Authentication
  description: This API uses OAuth 2.0 for secure authentication.
paths:
  /oauth/authorization:
    get:
      tags:
      - Authentication
      summary: Validate OAuth Token
      description: 'Validates the `Authorization: Bearer XXXX` OAuth 2.0 token header and returns a successful response

        with `client_id` and `user_id` or fails if it''s invalid.'
      operationId: oauth_token_validate
      responses:
        '200':
          description: Successful
          content:
            application/json:
              schema:
                required:
                - client_id
                - scopes
                properties:
                  client_id:
                    $ref: '#/components/schemas/UUID'
                  scopes:
                    type: array
                    items:
                      type: string
                    default: []
                type: object
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/Forbidden'
        default:
          $ref: '#/components/responses/ServerError'
  /oauth/token:
    post:
      tags:
      - Authentication
      summary: Request OAuth Token
      description: '### Flow


        The client sends a POST request with following body parameters to the authorization server:


        * `grant_type` with the value `client_credentials`

        * `client_id` with the client''s ID

        * `client_secret` with the client''s secret


        The authorization server will respond with a JSON object containing the following properties:


        * `token_type` with the value `Bearer`

        * `expires_in` with an integer representing the TTL (in seconds) of the access token (Default is 8 hours)

        * `access_token` a JWT signed with the authorization server''s private key


        The `access_token` should be used in the `Authorization` header together with the `Bearer` challenge to authenticate all the requests.


        > Example: `Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c`.'
      operationId: oauth_token_create
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/OauthClientCredentialsGrantRequestBodyParams'
      responses:
        '200':
          description: Successful
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/OauthTokenResponseBody'
  /oauth/token/revoke:
    post:
      tags:
      - Authentication
      summary: Revoke OAuth Token
      description: 'Revokes the oAuth token using the token from the `Authorization: Bearer XXXX` header and returns a 204 response'
      operationId: oauth_token_revoke
      parameters:
      - name: authorization
        in: header
        description: Authorization Header with Token
        required: true
        schema:
          type: string
      responses:
        '200':
          description: Successful
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/Forbidden'
        default:
          $ref: '#/components/responses/ServerError'
components:
  schemas:
    OauthTokenResponseBody:
      title: Request Oauth Token Response
      properties:
        token_type:
          type: string
          example: Bearer
        expires_in:
          description: TTL of the access token in seconds (Default is 8 hours)
          type: integer
        access_token:
          description: JWT signed with the authorization server's private key
          type: string
      type: object
    OauthClientCredentialsGrantRequestBodyParams:
      title: Request OAuth Token
      required:
      - grant_type
      - client_id
      - client_secret
      properties:
        grant_type:
          type: string
          example: client_credentials
        client_id:
          $ref: '#/components/schemas/UUID'
        client_secret:
          type: string
      type: object
    UUID:
      type: string
      format: uuid
      maxLength: 36
      minLength: 36
      example: 12345667-890a-bcde-f123-34567890abcd
    ErrorsObject:
      title: API Errors
      properties:
        errors:
          type: array
          items:
            required:
            - title
            - code
            properties:
              title:
                description: Error message
                type: string
              code:
                description: Error code
                type:
                - string
                - 'null'
              source:
                description: Property path where the error occurred, if applicable
                type:
                - string
                - 'null'
            type: object
      type: object
  responses:
    Forbidden:
      description: Forbidden Request. The operation cannot be completed.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorsObject'
    ServerError:
      description: Unexpected Server Error
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorsObject'
    Unauthorized:
      description: Unauthorized request or invalid credentials
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorsObject'
  securitySchemes:
    oauth2:
      type: oauth2
      description: 'This authentication mechanism is based on the OAuth 2.0 prototocol and requires a Client ID, a Client Secret Key and

        in some cases also a user and password.


        With these credentials, the client should request a token using the `POST /api/v1/oauth/token` endpoint,

        which should be used in the `Authorization` header together with the `Bearer` challenge to authenticate all the requests.


        > Example: `Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c`.'
      flows:
        password:
          tokenUrl: /oauth/token
          scopes:
            default: default
x-provenance:
  method: searched
  source: https://docs.billie.io/reference
  harvested: '2026-10-14'
  tool: harvest-readme-openapi.py
  note: Assembled verbatim from the OpenAPI definition ReadMe embeds in each operation page of the provider's developer portal; paths and components merged by API title, nothing authored.
  assembled_from:
  - https://docs.billie.io/reference/confirm_authorization_v2.md
  - https://docs.billie.io/reference/create_checkout_session_v2.md
  - https://docs.billie.io/reference/create_credit_note.md
  - https://docs.billie.io/reference/create_hpp_checkout_session_v2.md
  - https://docs.billie.io/reference/get_checkout_session_authorization_v2.md
  - https://docs.billie.io/reference/get_invoice.md
  - https://docs.billie.io/reference/get_legal_forms.md
  - https://docs.billie.io/reference/invoice_cancel_v2.md
  - https://docs.billie.io/reference/invoice_create.md
  - https://docs.billie.io/reference/invoice_payment_confirm.md
  - https://docs.billie.io/reference/invoice_update.md
  - https://docs.billie.io/reference/oauth_token_create.md
  - https://docs.billie.io/reference/oauth_token_revoke.md
  - https://docs.billie.io/reference/oauth_token_validate.md
  - https://docs.billie.io/reference/order_cancel_v2.md
  - https://docs.billie.io/reference/order_create_v2.md
  - https://docs.billie.io/reference/order_get_details_v2.md
  - https://docs.billie.io/reference/order_update_v2.md
  merge:
    pages: 18
    deduped: 152
    conflicts_kept_first: 0

Billie Authentication API

Operations 3

Documentation

Specifications

Schemas & Data

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