# Handle buyer checkout errors

Use `onError` callbacks and alternate checkout pages to handle buyer checkout errors.

## Know before you code

### PayPal Checkout

Complete the steps in **Get started** to get your sandbox account login information and access token from the Developer Dashboard.

This feature modifies an existing PayPal Checkout integration and uses the following:

- [JavaScript SDK](/sdk/js/) Adds PayPal-supported payment methods.
- [Orders REST API](/docs/api/orders/v2/) Create, update, retrieve, authorize, and capture orders.

### Explore PayPal APIs with Postman

You can use Postman to explore and test PayPal APIs. Learn more in our [Postman guide](/api/rest/postman).

If an error prevents buyer checkout, alert the user that an error has occurred with the buttons using the `onError` callback.

#### **`Buyer checkout error`**

```javascript
paypal.Buttons({
    onError: function(err) {
        // For example, redirect to a specific error page
        window.location.href = "/your-error-page-here";
    }
}).render('#paypal-button-container');
```

This error handler is a catch-all. Errors at this point are not expected to be handled beyond showing a generic error message or page.

If null pointer errors prevent the script from loading, provide a different checkout experience.

#### **`Script not loading error`**

```javascript
if (window.paypal && window.paypal.Buttons) {
    // render the buttons
} else {
    // show a fallback experience
}
```