> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agentaos.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Change the plan
> Apply a plan change quoted by the preview. Echo the preview's `prorationDate` so the amount charged matches the quote. An upgrade charges the prorated difference on the saved card now and the response carries the new per-cycle amount; a downgrade is scheduled for the current period end (`effectiveAt`) and charges nothing today. Idempotent on (subscription, target plan, prorationDate). Same plan, a non-active subscription, a different currency, or a different billing interval return `400`.
An **upgrade** charges the prorated difference on the subscriber's saved card **now**. Always show the [preview](/api-reference/subscriptions/plan-change-preview) first and echo its `prorationDate`; that is what makes the charge equal the quote. A **downgrade** charges nothing today and switches at the current period end.
Idempotent on (subscription, target plan, `prorationDate`): retrying the same request does not charge twice. Same plan, a subscription that is not `active` or `trialing`, a different currency, or a different billing interval return `400`.
## OpenAPI
````yaml POST /gateway/subscriptions/{id}/plan-change
openapi: 3.1.0
info:
title: AgentaOS Gateway API
version: 1.0.0
description: >-
The AgentaOS REST API: payment links, checkouts, subscriptions, customers,
invoices, and the unified transactions feed. This is the same API the
TypeScript SDK (`@agentaos/pay`) and the `agenta` CLI call underneath.
## Money model
- **Decimal currency units (`number`)**: a plain `amount` field (on a create
body, a Payment Link, a Checkout's `amount_override`, or an Invoice's
`amount`/`fiat_amount`/`tax_amount`) is in currency units. `49.99` means EUR
49.99, never cents.
- **Integer minor units (`number`)**: exactly one field breaks that rule:
`unitAmountMinor` on a Subscription. It is an integer count of the smallest
currency unit (`1999` means EUR 19.99), named with a `Minor` suffix
specifically so it is never confused with a plain `amount`. The `money`
object on Transactions and the `earnings` object on a retrieved Invoice are
also integer minor units, computed server-side.
- **String, on webhooks**: the `amount` inside a webhook payload's `data`
object is a string (e.g. `"49.99"`), since JSON numbers silently drop
trailing zeros and this value must round-trip exactly for accounting.
## Naming convention
Most response fields mirror the underlying database column and are
`snake_case` (`created_at`, `seller_mode`, `buyer_email`, ...). A small
number of computed convenience fields are camelCase with no snake_case
equivalent: `checkoutUrl` on Checkouts and Payment Links, `sellerMode` on
Payment Links specifically, `money` on Transactions, and `earnings` on a
single retrieved Invoice. Two resources (Subscriptions and Customers) are
fully camelCase end to end.
## Pagination
Every list endpoint takes `limit` and `offset` and returns `{ items, total,
hasMore }`. `hasMore` is computed server-side (`offset + items.length <
total`); never derive it client-side.
contact:
name: AgentaOS
url: https://agentaos.ai
license:
name: Proprietary
url: https://agentaos.ai
servers:
- url: https://api.agentaos.ai/api/v1
description: Production
security:
- ApiKeyAuth: []
tags:
- name: Payment Links
description: >-
Reusable, shareable payment products: a fixed amount and description
behind one URL.
- name: Checkouts
description: >-
One attempt to collect one payment, standalone or built from a payment
link. Wire path is `/gateway/sessions`; the SDK and CLI call this resource
"checkout".
- name: Subscriptions
description: >-
Merchant-side read and management surface for recurring plans. Created
automatically when a buyer pays a `type: subscription` payment link.
- name: Customers
description: 'Read-only surface: everyone who has paid you or been sent an invoice.'
- name: Invoices
description: >-
Every checkout issues an invoice. List, retrieve, void, export, and
download PDFs/receipts.
- name: Transactions
description: >-
The unified activity feed: every inbound payment and outbound send, across
every rail, in one list.
paths:
/gateway/subscriptions/{id}/plan-change:
post:
tags:
- Subscriptions
summary: Change the plan
description: >-
Apply a plan change quoted by the preview. Echo the preview's
`prorationDate` so the amount charged matches the quote. An upgrade
charges the prorated difference on the saved card now and the response
carries the new per-cycle amount; a downgrade is scheduled for the
current period end (`effectiveAt`) and charges nothing today. Idempotent
on (subscription, target plan, prorationDate). Same plan, a non-active
subscription, a different currency, or a different billing interval
return `400`.
operationId: changeSubscriptionPlan
parameters:
- name: id
in: path
required: true
description: Subscription id.
schema:
type: string
format: uuid
requestBody:
required: true
content:
application/json:
schema:
$ref: '#/components/schemas/PlanChangeRequest'
example:
targetLinkId: c9e44cf2-b3c3-465c-8ab8-de0706be4974
prorationDate: 1788434542
responses:
'200':
description: The applied change. Shape depends on `direction`.
content:
application/json:
schema:
$ref: '#/components/schemas/PlanChangeResponse'
examples:
upgrade:
value:
direction: upgrade
applied: true
status: active
unitAmountMinor: 4900
currency: eur
downgrade:
value:
direction: downgrade
applied: true
effectiveAt: '2026-10-03T10:45:13.000Z'
unitAmountMinor: 2900
currency: eur
'400':
$ref: '#/components/responses/BadRequest'
'401':
$ref: '#/components/responses/Unauthorized'
'403':
$ref: '#/components/responses/Forbidden'
'404':
$ref: '#/components/responses/NotFound'
components:
schemas:
PlanChangeRequest:
type: object
properties:
targetLinkId:
type: string
format: uuid
description: The target product's payment-link id.
prorationDate:
type: integer
minimum: 1
description: From the preview response.
required:
- targetLinkId
- prorationDate
PlanChangeResponse:
oneOf:
- type: object
title: Upgrade applied
properties:
direction:
type: string
enum:
- upgrade
applied:
type: boolean
enum:
- true
status:
type: string
description: Subscription status after the change.
unitAmountMinor:
type: integer
description: New per-cycle amount.
currency:
type: string
required:
- direction
- applied
- status
- unitAmountMinor
- currency
- type: object
title: Downgrade scheduled
properties:
direction:
type: string
enum:
- downgrade
applied:
type: boolean
enum:
- true
effectiveAt:
type: string
format: date-time
description: >-
When the new plan starts: the current period end. Until then the
subscription keeps its current plan and reports the change as
`pendingPlanChange`.
unitAmountMinor:
type: integer
description: Per-cycle amount from `effectiveAt` on.
currency:
type: string
required:
- direction
- applied
- effectiveAt
- unitAmountMinor
- currency
- type: object
title: Pending downgrade reverted
properties:
direction:
type: string
enum:
- revert
applied:
type: boolean
enum:
- true
unitAmountMinor:
type: integer
description: The current plan's per-cycle amount, unchanged.
currency:
type: string
required:
- direction
- applied
- unitAmountMinor
- currency
Error:
type: object
description: >-
Every non-2xx response is JSON in this shape. Every response (success or
error) also carries an `x-request-id` response header; send that header
on your request to have your own id echoed back, otherwise the server
mints one. On errors the same id is repeated in the `requestId` body
field.
properties:
statusCode:
type: integer
description: Same as the HTTP status code.
message:
description: >-
Human-readable. A validation failure (400) returns an array of
per-field messages instead of one string.
anyOf:
- type: string
- type: array
items:
type: string
errors:
type: array
description: >-
Present on 400 validation failures: one entry per invalid field. The
flat human-readable strings stay in `message` for back-compat; this
is the machine-readable, per-field view.
items:
type: object
properties:
field:
type: string
description: >-
Name of the invalid field, dot-notated for nested properties
(e.g. `checkoutFields.0.type`).
message:
type: string
description: Validation messages for that field, joined with `, `.
required:
- field
- message
requestId:
type: string
description: >-
Correlation id, identical to the `x-request-id` response header.
Include it when contacting support. On success it is available on
the header only, not the body.
timestamp:
type: string
format: date-time
required:
- statusCode
- message
- timestamp
responses:
BadRequest:
description: >-
A required field is missing, out of range, or the wrong type.
`ValidationPipe` also rejects any field not in the documented schema.
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
example:
statusCode: 400
message: amount is required when creating a session without a link
timestamp: '2026-08-06T12:00:00.000Z'
Unauthorized:
description: Missing or invalid `x-api-key`.
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
example:
statusCode: 401
message: Invalid API key
timestamp: '2026-08-06T12:00:00.000Z'
Forbidden:
description: The key is valid but the resource belongs to a different organization.
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
example:
statusCode: 403
message: Payment link belongs to another organization
timestamp: '2026-08-06T12:00:00.000Z'
NotFound:
description: >-
Resource not found (or not visible to your key; the two are not
distinguished).
content:
application/json:
schema:
$ref: '#/components/schemas/Error'
example:
statusCode: 404
message: Payment link not found
timestamp: '2026-08-06T12:00:00.000Z'
securitySchemes:
ApiKeyAuth:
type: apiKey
in: header
name: x-api-key
description: >-
Your secret key, from app.agentaos.ai -> Settings -> Developers -> API
Keys. The key's prefix is both its identity and its environment:
`sk_test_...` (sandbox, free, no verification) or `sk_live_...` (real
money, requires business verification). A missing or invalid key returns
401.
````