## Run server update

Use this method to wrap an async function that makes a request to your server to update the Checkout Session.

> `runServerUpdate` enforces a 20-second timeout for your update function. If your function doesn't resolve within 20 seconds, `runServerUpdate` returns an error. Wrap `runServerUpdate` calls in `try`/`catch` blocks to handle any errors.

This method returns a `Promise` that resolves with an object containing the following fields:
* `type`: one of either `"success"` or `"error"`
* `session`: only populated when `type` is `"success"`. Contains a [Session](/js/custom_checkout/session_object) instance representing the updated state.
* `error`: only populated when `type` is `"error"`. Contains an object with a string `message` field which can be displayed to your customer.

**Syntax:** `actions.runServerUpdate(...)`

- `userFunction` (function) **required**
  An async function to make a request to your server to update the Checkout Session.

### Run server update

```jsx
actions.runServerUpdate(
  () => {
    return fetch('/update-checkout-session', {
      method: 'POST',
      body: JSON.stringify({checkoutSessionId: '{CHECKOUT_SESSION_ID}'}),
    });
  }
);
```