> ## Documentation Index > Fetch the complete documentation index at: https://commet.co/docs/llms.txt > Use this file to discover all available pages before exploring further. # Pay billing periods in advance > Creates a hosted checkout to pay billing periods of a recurring subscription in advance with any payment method. On an active subscription the paid periods start after the last paid period and replace any open prepaid-periods checkout. On a pending-payment subscription the first payment covers the requested periods and replaces its pending checkout. The billing interval does not change. > [!NOTE] > > This reference describes API version `2026-08-27`. Send `Commet-Version: 2026-08-27` with your request. ## OpenAPI ````yaml /openapi/en/rest/2026-08-27.json post /subscriptions/{id}/prepaid-periods openapi: 3.1.0 info: title: Commet API version: '2026-08-27' description: Billing and payments API for SaaS and AI products. servers: - url: https://commet.co/api/v1 security: - ApiKeyAuth: [] tags: - name: Test Clock description: >- Simulate the passage of time in sandbox to test billing flows. Mirrors Stripe test clocks: forward-only and sandbox-only. - name: Customers - name: Subscriptions - name: Plans - name: Markets description: >- Reusable country groups for market-specific prices and selectable price variants. - name: Offers - name: Promo Codes - name: Features - name: Usage - name: Seats - name: Quota - name: Add-ons - name: Portal - name: Credit Packs - name: Plan Groups - name: Invoices - name: Payments description: >- One-time payments with no subscription or plan. Charge a customer's saved payment method off-session, or create a payment link the customer opens to pay. Tax, invoice, and receipt are handled automatically. - name: Transactions - name: Webhooks - name: API Keys - name: Payouts description: >- Withdraw available balance to your bank and manage the payout account (verification + destination bank accounts). - name: Provisioning description: >- Take ownership of an organization an agent provisioned headlessly. The agent holds the API keys from the start; a human claims the account through a claim link. paths: /subscriptions/{id}/prepaid-periods: post: tags: - Subscriptions summary: Pay billing periods in advance description: >- Creates a hosted checkout to pay billing periods of a recurring subscription in advance with any payment method. On an active subscription the paid periods start after the last paid period and replace any open prepaid-periods checkout. On a pending-payment subscription the first payment covers the requested periods and replaces its pending checkout. The billing interval does not change. operationId: create-prepaid-periods-checkout parameters: - name: Idempotency-Key in: header required: false description: >- Unique key used to safely retry this write for 24 hours without applying it twice. schema: type: string minLength: 1 maxLength: 200 - name: id in: path required: true schema: type: string - name: Commet-Version in: header required: false description: >- API version used by this reference. Send this header to select this contract explicitly. schema: type: string default: '2026-08-27' example: '2026-08-27' requestBody: required: true content: application/json: schema: type: object properties: periods: type: integer minimum: 1 maximum: 60 description: >- Active subscriptions: billing periods to add after the last paid period. Pending-payment subscriptions: total billing periods the first payment covers, including the current one. offerId: description: >- Offer applied from the first added period for its full configured duration. Active subscriptions only; assign an Offer to a pending-payment subscription with PUT /subscriptions/{id}/offer. type: string minLength: 1 successUrl: type: string format: uri required: - periods responses: '200': description: Success headers: X-Request-Id: $ref: '#/components/headers/RequestId' RateLimit-Limit: description: Maximum number of requests allowed in the current window. schema: type: string RateLimit-Remaining: description: Requests remaining in the current window. schema: type: string content: application/json: schema: $ref: '#/components/schemas/PrepaidPeriodsCheckout' example: checkoutUrl: https://commet.co/checkout/example_prepaid_periods_token object: checkout_session livemode: false '400': description: Bad request headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: validation_error code: validation_error message: The request contains an invalid parameter. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/validation_error.md '401': description: Unauthorized headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: authentication_error code: unauthorized message: A valid API key is required. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/unauthorized.md '403': description: Forbidden headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: authentication_error code: forbidden message: You do not have permission to perform this operation. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/forbidden.md '404': description: Not found headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: not_found_error code: not_found message: The requested resource was not found. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/not_found.md '409': description: Conflict headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: conflict_error code: idempotency_in_progress message: >- A request with this idempotency key is still being processed. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/idempotency_in_progress.md '429': description: Too many requests headers: X-Request-Id: $ref: '#/components/headers/RequestId' RateLimit-Limit: description: Maximum number of requests allowed in the current window. schema: type: string RateLimit-Remaining: description: Requests remaining in the current window. schema: type: string RateLimit-Reset: description: Seconds until the rate limit window resets. schema: type: string Retry-After: description: Seconds to wait before retrying the request. schema: type: string content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: rate_limit_error code: rate_limited message: >- Too many requests. Retry after the interval specified in the Retry-After header. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/rate_limited.md '500': description: Internal server error headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: internal_error code: internal_error message: An unexpected error occurred while processing the request. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/internal_error.md '503': description: Service unavailable headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: error: type: internal_error code: idempotency_unavailable message: >- Idempotency storage is temporarily unavailable. Retry with the same idempotency key. doc_url: >- https://commet.co/docs/api-reference/2026-08-27/errors/idempotency_unavailable.md components: headers: RequestId: description: >- Server-generated identifier that correlates this response with Platform logs. schema: type: string format: uuid schemas: PrepaidPeriodsCheckout: type: object properties: checkoutUrl: type: string object: type: string const: checkout_session livemode: type: boolean required: - checkoutUrl - object - livemode additionalProperties: false ErrorResponse: type: object properties: error: type: object properties: type: type: string code: type: string message: type: string param: type: string details: {} doc_url: type: string required: - type - code - message - doc_url additionalProperties: false required: - error additionalProperties: false securitySchemes: ApiKeyAuth: type: apiKey in: header name: x-api-key ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.