update-plan-amount.mdx

title	update_plan_amount
description	Updates the billing amount of an existing plan. The new amount must stay within the price ceiling that subscribers agreed to, so no re-authorization is needed.

fn update_plan_amount(env: Env, plan_id: u64, new_amount: i128)

Updates the per-period billing amount of an existing plan. The new amount must be positive and must not exceed the plan's price_ceiling. This allows merchants to adjust pricing without requiring subscribers to re-authorize.

---

Parameters

Name	Type	Description
plan_id	u64	The ID of the plan to update.
new_amount	i128	The new billing amount per period, in stroops.

---

Authorization

merchant.require_auth();

The merchant address stored on the plan must sign the transaction.

---

Return value

None (void).

---

Events emitted

Event	Topics	Data
plan_updated	plan_id, new_amount	Updated plan details

---

Error cases

Code	Name	Description
6	PlanNotFound	No plan exists with the given plan_id.
3	InvalidAmount	new_amount is zero or negative.
10	AmountExceedsCeiling	new_amount exceeds the plan's price_ceiling.

---

Examples

```typescript import { VowenaClient, NETWORKS, toStroops } from "@vowena/sdk";

const client = new VowenaClient({
  contractId: NETWORKS.testnet.contractId,
  rpcUrl: NETWORKS.testnet.rpcUrl,
  networkPassphrase: NETWORKS.testnet.networkPassphrase,
});

// Raise the price from 9.99 to 12.99 (within the 14.99 ceiling)
const tx = await client.buildUpdatePlanAmount(
  planId,                   // Plan ID
  toStroops("12.99")        // 129900000n stroops
);

const signedXdr = await signTransaction(tx);
await client.submitTransaction(signedXdr);
```

```bash soroban contract invoke \ --id CONTRACT_ID \ --network testnet \ --source MERCHANT_SECRET \ -- \ update_plan_amount \ --plan_id 1 \ --new_amount 129900000 ``` Since the token allowance is set against the `price_ceiling` (not the current `amount`), updating the amount within the ceiling does not require subscribers to re-authorize. All existing subscriptions will be charged the new amount on their next billing cycle. If you need to set a price above the current ceiling, you must create a new plan and use the [migration flow](/api-reference/request-migration) to move subscribers. This ensures subscribers always have explicit control over their maximum exposure.