> ## 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. # Preview a plan change > Quote moving a subscription to another plan. Read-only: nothing is charged or scheduled. The target must be a different subscription product in the same currency and billing interval, and the subscription must be `active` or `trialing`. An upgrade (higher price) is charged now, prorated; a downgrade switches at the current period end with nothing due today. Pass the returned `prorationDate` to the apply call so the charge matches this quote. Read-only. Nothing is charged or scheduled until you call [Change the plan](/api-reference/subscriptions/plan-change) with the `prorationDate` from this response. The target must be a different subscription product in the same currency and billing interval; the subscription must be `active` or `trialing`. Anything else returns `400`. ## OpenAPI ````yaml GET /gateway/subscriptions/{id}/plan-change/preview 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/preview: get: tags: - Subscriptions summary: Preview a plan change description: >- Quote moving a subscription to another plan. Read-only: nothing is charged or scheduled. The target must be a different subscription product in the same currency and billing interval, and the subscription must be `active` or `trialing`. An upgrade (higher price) is charged now, prorated; a downgrade switches at the current period end with nothing due today. Pass the returned `prorationDate` to the apply call so the charge matches this quote. operationId: previewSubscriptionPlanChange parameters: - name: id in: path required: true description: Subscription id. schema: type: string format: uuid - name: targetLinkId in: query required: true description: The target product's payment-link id. schema: type: string format: uuid responses: '200': description: The quote. Money fields are integer minor units. content: application/json: schema: $ref: '#/components/schemas/PlanChangePreview' example: direction: upgrade currency: eur dueTodayMinor: 1234 dueTodayVatMinor: 239 effectiveAt: '2026-09-03T10:31:25.000Z' nextInvoiceMinor: 4900 nextInvoiceVatMinor: 1176 nextInvoiceAt: '2026-10-03T10:45:13.000Z' prorationDate: 1788434542 '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/NotFound' components: schemas: PlanChangePreview: type: object description: >- Read-only quote for moving a subscription to another plan. Money is integer minor units. properties: direction: type: string enum: - upgrade - downgrade - revert description: >- `upgrade` when the new plan costs more per cycle; `downgrade` otherwise; `revert` when the target is the current plan while a downgrade is pending (cancels it, nothing due). currency: type: string dueTodayMinor: type: integer description: Charged now. Always 0 for a downgrade. dueTodayVatMinor: type: integer effectiveAt: type: string format: date-time description: 'Upgrade: now. Downgrade: the current period end.' nextInvoiceMinor: type: integer description: The next regular cycle invoice on the new plan. nextInvoiceVatMinor: type: integer nextInvoiceAt: type: string format: date-time prorationDate: type: integer description: >- Unix seconds. Echo it in the apply request so the charge matches this quote. required: - direction - currency - dueTodayMinor - dueTodayVatMinor - effectiveAt - nextInvoiceMinor - nextInvoiceVatMinor - nextInvoiceAt - prorationDate 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. ````