DocsAPI reference

Change plan

Moves an existing subscription to another plan, prorated, in place.

post/api/billing/change-plan
Authentication
Bearer token
Retries
Idempotency-Key
Body
application/json
Version
2026-09-03

Answers with one of two things for the browser to do:

payment_link the bank wants the customer to authorise the charge - send the browser there; the plan changes when the provider's webhook reports the payment pending the provider accepted it; the plan changes when its subscription.plan_changed webhook lands, usually in seconds, so the screen watches the subscription

The tier is NEVER changed here. A declined proration charge keeps the old plan (on_payment_failure: prevent_change), and only the webhook knows which way it went.

Headers#

  • Idempotency-Keystring

    A unique key of your choosing, so this request can be retried safely. The first request with a given key executes; every replay returns that first response unchanged, with Idempotent-Replay: true set.

    Generate one key per action, not per session - reusing a key with a different body is refused with 422 rather than silently replaying the wrong answer. Keys are remembered for 24 hours. A request that failed releases its key, so a retry after fixing the payload runs normally.

    Up to 255 characters

Request body#

application/json · required

ChangePlanRequest

  • tierstringrequired

    One of the purchasable tiers

Responses#

  • 200OKapplication/json

    object

    5 response headers
    RateLimit-Limit

    Requests permitted in the current window.

    RateLimit-Remaining

    Requests left in the current window. Back off before it reaches 0.

    RateLimit-Reset

    Seconds until the current window resets.

    X-API-Version

    The dated version of the API contract that served this response, e.g. 2026-09-03. Pin against it; it changes only when a response shape changes incompatibly.

    X-Request-ID

    Quote this in a support request to identify the call.

  • 422Validation error

    The shared error envelope, served as application/problem+json with error.code set to validation_error. Its details name each field that failed and why.

Errors#

Failures use one envelope on every endpoint, described in Retries, versioning and limits. The codes you are most likely to meet here:

  • validation_error · 422 — The payload was well-formed JSON but failed schema validation.
  • unauthenticated · 401 — The request carried no API key, or one the API could not verify.
  • forbidden · 403 — The key is valid, but it is not allowed to do this — either the scope is missing or the resource belongs to another workspace.
  • idempotency_key_reused · 422 — This `Idempotency-Key` was used before, for a request with a different body.
  • rate_limited · 429 — Too many requests in the current window. The limit is per workspace, and some endpoints add a per-agent limit on top.

More Billing endpoints#

Something unclear or missing? Tell us and we’ll fix it.