> ## Documentation Index
> Fetch the complete documentation index at: https://vowena.xyz/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# update_plan_amount

> 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.

```rust theme={null}
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

```rust theme={null}
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

<Tabs>
  <Tab title="SDK">
    ```typescript theme={null}
    import { VowenaClient, NETWORKS, toStroops } from "@vowena/sdk";

    const client = new VowenaClient({
      contractId: NETWORKS.mainnet.contractId,
      rpcUrl: NETWORKS.mainnet.rpcUrl,
      networkPassphrase: NETWORKS.mainnet.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);
    ```
  </Tab>

  <Tab title="Soroban CLI">
    ```bash theme={null}
    soroban contract invoke \
      --id CONTRACT_ID \
      --network mainnet \
      --source MERCHANT_SECRET \
      -- \
      update_plan_amount \
      --plan_id 1 \
      --new_amount 129900000
    ```
  </Tab>
</Tabs>

<Tip>
  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.
</Tip>

<Note>
  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.
</Note>