> ## Documentation Index > Fetch the complete documentation index at: https://docs.beinfi.com/llms.txt > Use this file to discover all available pages before exploring further. # Create a subscription > Subscribes the customer to the product and opens the first billing period. The response carries the subscription and that period. `customerId` is the customer's product enrollment id (from `POST /metering/products/{productID}/customers`), not the customer id. ## OpenAPI ````yaml /api-reference/openapi.en.json post /billing/products/{productID}/subscriptions openapi: 3.1.0 info: title: Infi API version: 0.0.1 description: > The Infi REST API: catalog, customers, usage metering, subscriptions, invoices, payments and checkout. **Authentication.** Send your secret key as `Authorization: Bearer sk_test_…` (sandbox) or `sk_live_…` (production). The key prefix selects the environment. Checkout routes (`/pay/*`) and `/public/*` take no key: they run in the payer's browser. **Idempotency.** Every request that changes data requires an `Idempotency-Key` header. A retry with the same key returns the original response instead of running again. **Amounts.** Money and quantities travel as decimal strings (`"150.00"`, `"0.0001"`), never as floating-point numbers. **Errors.** The body carries `error_code` (stable, branch on it), `message` (for humans) and `tracer_id` (send it to support). Rate-limit and idempotency errors are nested under `error`, with `code` and `request_id`. servers: - url: https://api-sandbox.beinfi.com description: Sandbox - url: https://api.beinfi.com description: Production security: - bearerAuth: [] tags: - name: Catalog - name: Customers - name: Metering - name: Subscriptions - name: Invoices - name: Payments - name: Checkout - name: Coupons - name: Billing - name: Account - name: Webhooks - name: Test account - name: Rail - name: Storefronts paths: /billing/products/{productID}/subscriptions: parameters: - $ref: '#/components/parameters/ProductID' post: tags: - Subscriptions summary: Create a subscription description: > Subscribes the customer to the product and opens the first billing period. The response carries the subscription and that period. `customerId` is the customer's product enrollment id (from `POST /metering/products/{productID}/customers`), not the customer id. operationId: createSubscription parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: type: object required: - customerId properties: customerId: type: string format: uuid description: The customer's enrollment id for this product. productVersionId: type: - string - 'null' format: uuid description: >- The product version the subscription bills. Defaults to the latest published version. anchor: type: - string - 'null' format: date-time description: >- When the billing cycle starts, which sets the day of later charges. Defaults to the time of creation. items: type: array items: type: object required: - kind properties: kind: type: string enum: - recurring_fee - credit_grant - metered_usage timing: type: - string - 'null' enum: - advance - arrears - null description: > What the subscription bills, item by item. Each item has a `kind`: `recurring_fee` (a fixed fee, with `timing` `advance` to bill at the start of the period or `arrears` to bill at the end; defaults to `advance`), `credit_grant` (credits granted each cycle) or `metered_usage` (metered usage, billed at the end of the period). Only `recurring_fee` takes `timing`. When omitted, items follow the product's pricing model: a prepaid product bills the fee up front and grants credits; any other bills the fee and usage at the end of the period. responses: '201': content: application/json: schema: type: object properties: subscription: $ref: '#/components/schemas/Subscription' period: $ref: '#/components/schemas/SubscriptionPeriod' description: Created. '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '422': $ref: '#/components/responses/ValidationFailed' components: parameters: ProductID: name: productID in: path required: true schema: type: string format: uuid description: Product ID. IdempotencyKey: name: Idempotency-Key in: header required: false schema: type: string description: >- A unique key per operation (a UUID works). Retrying with the same key returns the original response. schemas: Subscription: type: object properties: id: type: string format: uuid customerId: type: string format: uuid description: Enrollment ID. productVersionId: type: string format: uuid description: >- The product version subscribed to. It sets the price billed, even if the product changes later. status: type: string enum: - trialing - active - past_due - paused - canceled billingCycle: type: string enum: - weekly - monthly - annual collectionMethod: type: string enum: - charge_automatically - send_invoice description: >- `charge_automatically` charges on its own; `send_invoice` sends the invoice for the customer to pay. billingMode: type: string enum: - arrears - advance description: '`advance` bills at the start of the period; `arrears`, at the end.' anchor: type: string format: date-time description: Reference date the billing periods are counted from. nextBillingDate: type: - string - 'null' format: date-time description: Next billing date. startedAt: type: string format: date-time canceledAt: type: - string - 'null' format: date-time items: type: array items: $ref: '#/components/schemas/SubscriptionItem' description: What the subscription bills or grants. SubscriptionPeriod: type: object properties: id: type: string format: uuid subscriptionId: type: string format: uuid periodStart: type: string format: date-time description: Start of the period (inclusive). periodEnd: type: string format: date-time description: End of the period (exclusive). status: type: string enum: - open - closed - invoiced description: >- `open` (collecting usage), `closed` (ended, invoice not generated yet) or `invoiced` (already billed). invoiceId: type: - string - 'null' format: uuid description: The invoice that billed this period description: >- One billing window of a subscription. Metered usage lands in the open period. SubscriptionItem: type: object properties: id: type: string format: uuid kind: type: string enum: - recurring_fee - credit_grant - metered_usage - prepaid_usage description: >- `recurring_fee` is the fixed recurring fee; `credit_grant`, credits granted each cycle; `metered_usage`, usage billed afterwards; `prepaid_usage`, usage paid upfront. timing: type: - string - 'null' enum: - advance - arrears - null description: '`advance` bills at the start of the period; `arrears`, at the end.' productVersionId: type: string format: uuid description: The product version the item comes from. createdAt: type: string format: date-time canceledAt: type: - string - 'null' format: date-time Error: type: object required: - message - error_code - tracer_id properties: message: type: string description: Human-readable sentence. error_code: $ref: '#/components/schemas/ErrorCode' description: Stable error code. Branch on it. tracer_id: type: string description: Request id. Include it when contacting support. description: >- The standard error body. It is flat (no `error` wrapper) and the trace id is `tracer_id`. ValidationError: type: object required: - message - error_code - tracer_id - errors properties: message: type: string error_code: $ref: '#/components/schemas/ErrorCode' tracer_id: type: string errors: type: array items: type: object required: - field - value - constraint - description properties: field: type: string value: type: string constraint: type: string description: type: string description: >- Per-field detail (`field`, `description`). Always present on a `422`; may be empty. description: >- Body of a `422`. Same shape as `Error`, plus `errors[]` with per-field detail. That is where the sentence telling you what to fix lives (for example, "product has no published version"). ErrorCode: type: string examples: - internal_error - validation_failed - bad_request - unauthorized - forbidden - not_found - conflict - rate_limited description: >- Stable error code. The list is open: besides the generic codes, each area defines its own (`coupon_expired`, `insufficient_balance`, `version_not_draft`, `idempotency_key_reused`…). Handle a code you do not recognize by its HTTP status and show `message`; do not fail parsing the response. responses: BadRequest: content: application/json: schema: $ref: '#/components/schemas/Error' description: Malformed request. Unauthorized: content: application/json: schema: $ref: '#/components/schemas/Error' description: Missing or invalid API key. ValidationFailed: content: application/json: schema: $ref: '#/components/schemas/ValidationError' description: One or more fields are invalid. Per-field detail is in `errors[]`. securitySchemes: bearerAuth: type: http scheme: bearer description: >- Your account's secret key: `Authorization: Bearer sk_test_…` or `sk_live_…`. Server-side only. ````