curl --request POST \
  --url https://commet.co/api/v1/subscriptions/{id}/change-plan \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "newPlanId": "<string>",
  "successUrl": "<string>",
  "offerId": "<string>"
}
'

import { Commet } from "@commet/node";

const commet = new Commet({ apiKey: "ck_xxx" });

const planChange = await commet.subscriptions.changePlan({ id: "sub_xxx" });

from commet import Commet

commet = Commet("ck_xxx")

plan_change = commet.subscriptions.change_plan("sub_xxx")

client, err := commet.New("ck_xxx")
if err != nil {
	log.Fatal(err)
}
ctx := context.Background()

planChange, err := client.Subscriptions.ChangePlan(ctx, "sub_xxx", nil)
if err != nil {
	log.Fatal(err)
}

import co.commet.Commet;
import co.commet.params.ChangePlanParams;

var commet = Commet.builder().apiKey("ck_xxx").build();

var planChange = commet.subscriptions().changePlan(
    "sub_xxx",
    ChangePlanParams.builder().build()
);

use Commet\Commet;

$commet = new Commet('ck_xxx');

$planChange = $commet->subscriptions->changePlan(id: 'sub_xxx');

{
  "outcome": "requires_checkout",
  "requiresCheckout": true,
  "checkoutUrl": "https://commet.co/checkout/example_plan_change_token",
  "object": "plan_change",
  "livemode": false
}

{
  "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"
  }
}

{
  "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"
  }
}

{
  "error": {
    "type": "billing_error",
    "code": "payment_failed",
    "message": "The payment could not be completed.",
    "doc_url": "https://commet.co/docs/api-reference/2026-08-27/errors/payment_failed.md"
  }
}

{
  "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"
  }
}

{
  "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"
  }
}

{
  "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"
  }
}

{
  "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"
  }
}

{
  "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"
  }
}

{
  "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"
  }
}