> ## Documentation Index > Fetch the complete documentation index at: https://docs-pos.solya.app/llms.txt > Use this file to discover all available pages before exploring further. # Open a Stripe Checkout session for a monthly plan > Opens a Stripe subscription Checkout session for the plan tier `tierId` and returns the session `id` plus the hosted `url` a human must be redirected to. THIS MUTATES A RECURRING SUBSCRIPTION once that page is paid: the tier is written onto the wallet and its monthly credits are granted by the `invoice.paid` webhook on every renewal, not by this call. Never call it to inspect or compare plans — the catalogue operation does that, and is also the only source of a valid `tierId`; an unknown tier 404s. When Stripe is unconfigured the session is a local stub (`dryRun: true`). ## OpenAPI ````yaml /openapi.json post /v1/credits/plan openapi: 3.0.3 info: title: Solya POS API version: 1.0.0 description: >- The Solya POS backend HTTP surface. Every documented operation is agent-ready: it carries an `operationId`, an agent-facing `description`, the `pos.*` scopes it enforces (`x-required-permissions`) and an `x-agent-tier`. Success responses return the payload as raw JSON; failures return the `ErrorResponse` envelope (`{ error: { code, message, statusCode } }`). servers: - url: / description: The backend, relative to its deployed origin. security: [] paths: /v1/credits/plan: post: tags: - Billing summary: Open a Stripe Checkout session for a monthly plan description: >- Opens a Stripe subscription Checkout session for the plan tier `tierId` and returns the session `id` plus the hosted `url` a human must be redirected to. THIS MUTATES A RECURRING SUBSCRIPTION once that page is paid: the tier is written onto the wallet and its monthly credits are granted by the `invoice.paid` webhook on every renewal, not by this call. Never call it to inspect or compare plans — the catalogue operation does that, and is also the only source of a valid `tierId`; an unknown tier 404s. When Stripe is unconfigured the session is a local stub (`dryRun: true`). operationId: openPlanCheckout requestBody: required: true content: application/json: schema: type: object properties: tierId: type: string minLength: 1 required: - tierId example: tierId: starter responses: '200': description: >- The opened subscription session. When Stripe is unconfigured this is instead a stub with `dryRun: true`, an empty `url` and id `cs_dryrun_plan_`. content: application/json: schema: type: object properties: id: type: string minLength: 1 url: type: string dryRun: type: boolean required: - id - url - dryRun additionalProperties: false description: >- The opened subscription session. When Stripe is unconfigured this is instead a stub with `dryRun: true`, an empty `url` and id `cs_dryrun_plan_`. example: id: cs_test_Z9y8X7w6V5u4T3s2 url: https://checkout.stripe.com/c/pay/cs_test_Z9y8X7w6V5u4T3s2 dryRun: false '400': description: >- The request failed schema validation; `error.fieldErrors` lists the fields. content: application/json: schema: $ref: '#/components/schemas/ValidationErrorResponse' '401': description: No valid credential was presented — send a bearer token. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '403': description: The actor is authenticated but lacks the required `pos.*` scope. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '404': description: No resource matches the addressed identifier. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '500': description: An unexpected server error — safe to retry idempotent requests. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - bearerAuth: [] components: schemas: ValidationErrorResponse: type: object required: - error additionalProperties: false description: >- A `VALIDATION_FAILED` envelope carrying the offending fields in `fieldErrors`. properties: error: type: object required: - code - message - statusCode additionalProperties: false properties: code: type: string enum: - VALIDATION_FAILED message: type: string statusCode: type: integer fieldErrors: type: array description: >- One entry per rejected field: the field path and why it was rejected. items: type: object required: - field - message additionalProperties: false properties: field: type: string description: Dot-path of the offending field. message: type: string description: Why the field was rejected. ErrorResponse: type: object required: - error additionalProperties: false description: The uniform failure envelope every non-2xx response returns. properties: error: type: object required: - code - message - statusCode additionalProperties: false properties: code: type: string enum: - VALIDATION_FAILED - UNAUTHORIZED - FORBIDDEN - NOT_FOUND - CONFLICT - BUSINESS_RULE_VIOLATION - INTERNAL_ERROR description: >- Machine-readable kernel `ResultCode` — branch on this, not on `message`. message: type: string description: >- Human-readable explanation. Safe to surface; never leaks server internals. statusCode: type: integer description: >- The HTTP status, mirrored into the body so a client need not read headers. securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: JWT description: >- `Authorization: Bearer `. Accepts EITHER a Keycloak access token (scopes-in-token) OR an opaque POS session token; both resolve to the same `pos.*` scope vocabulary the route guards enforce. ````