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

# Start a subscription



## OpenAPI

````yaml /openapi.json post /api/billing/checkout
openapi: 3.1.0
info:
  title: kealink API
  version: '2026-08-21'
  description: >-
    Permanent link shortening and dynamic QR codes.


    **A code we issue never stops resolving.** Not when the destination changes,
    not

    when a subscription lapses, not when the link is archived. Customers print
    these

    on physical materials, so a dead redirect is a reprint bill. Every design

    decision below follows from that.


    ### Authentication


    Send an API key as `Authorization: Bearer klk_...`. Mint one with

    `POST /api/billing/claim`. Keys are stored hashed and shown exactly once.


    ### Paying as an agent


    You do not need an account. `POST /api/links` with no credentials answers

    `402` with a machine-payment challenge — MPP (`WWW-Authenticate: Payment`)
    and

    x402 (`PAYMENT-REQUIRED`) on the same response. Pay either one, retry, and
    you

    get a permanent link plus an API key to repoint it with later.


    ### Errors


    Always `{ "error": "a sentence" }` with a real status code. `402` means this

    action needs payment — never that existing links stopped working.
  contact:
    name: kealink support
    url: https://kealinks.com
servers:
  - url: https://api.kealinks.com
    description: Production
security: []
tags:
  - name: Links
    description: Create and repoint permanent codes.
  - name: QR codes
    description: Print-ready artwork for a link.
  - name: Analytics
    description: Scans and clicks, by day, country, device or referrer.
  - name: Domains
    description: Serve your codes on your own hostname.
  - name: Account
    description: Tier, quota and what this account may do.
  - name: Billing
    description: Subscription lifecycle.
  - name: Team
    description: Workspaces and members.
  - name: Machine payments
    description: Buy a permanent link with no account, over MPP or x402. Built for agents.
  - name: Meta
    description: Discovery and health.
paths:
  /api/billing/checkout:
    post:
      tags:
        - Billing
      summary: Start a subscription
      operationId: createCheckoutSession
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CheckoutRequest'
      responses:
        '200':
          description: A Checkout URL to send the customer to.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CheckoutSession'
        '400':
          description: The request body or query string did not validate.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '401':
          description: Missing or invalid credentials.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '502':
          description: Checkout could not be started.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
      security:
        - bearerAuth: []
components:
  schemas:
    CheckoutRequest:
      type: object
      properties:
        plan:
          type: string
          enum:
            - starter
            - unlimited
        interval:
          type: string
          enum:
            - monthly
            - yearly
      additionalProperties: false
      description: >-
        Which plan to subscribe to, and how often to bill it. `starter` is
        A$19/month for 100 new links per billing cycle; `unlimited` is
        A$49/month or A$490/year with no per-cycle cap. Both include custom
        domains, scan analytics and teammates — the plans differ only in volume.
        Defaults to `unlimited` billed `monthly`. The starter plan is monthly
        only; asking for it yearly is a 400.
    CheckoutSession:
      type: object
      properties:
        url:
          type: string
          description: Send the customer here to complete payment.
          format: uri
      required:
        - url
      additionalProperties: false
    Error:
      type: object
      properties:
        error:
          type: string
          description: A sentence you can show a human. Never a code to switch on.
          examples:
            - Your subscription is inactive. Existing links keep resolving.
      required:
        - error
      additionalProperties: false
      description: >-
        Every failure returns this shape with a real status code. 402
        specifically means 'inactive subscription, existing links still work' —
        the message says so.
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: >-
        An API key (`klk_...`) or a Clerk session token. Both resolve to the
        same account and behave identically.

````