> For the complete documentation index, see [llms.txt](https://docs.rewst.help/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rewst.help/documentation/automations/intro-to-triggers/use-cases-and-examples/configure-a-webhook-trigger-for-cors-requests.md).
# Configure a webhook trigger for CORS requests
{% hint style="info" %}
Though this is related to triggers, it's most often used in conjunction with App Builder. Learn more about Rewst's App Builder in our documentation [here](/documentation/app-builder.md).
{% endhint %}
## What is a CORS request?
When referencing a Rewst web hook in JavaScript in an App Builder page— or outside of Rewst— you may see the error `TypeError: Failed to fetch.` This happens when the browser blocks your request because it does not allow *cross-origin* requests by default.
To make your webhook accessible from a web page, you must configure *CORS (Cross-Origin Resource Sharing)* headers and enable OPTIONS requests on your webhook.
{% hint style="info" %}
Note that **wait for webhook** cannot be set to `true` for this to work. Additionally, this webhook shouldn't use a secret key.
{% endhint %}
## Add CORS headers to your web hook response
1. Open your webhook trigger inside the workflow.
2. Click  to open the response headers code editor.
3. Add the following headers:
```django
{
"Content-Type": "application/json",
"Access-Control-Allow-Origin": "https://YOURDOMAINHERE",
"Access-Control-Allow-Methods": "POST, GET, OPTIONS",
"Access-Control-Allow-Headers": "Content-Type"
}
```
{% hint style="warning" %}
**Important -** Match the *exact* origin of your site.
> ✅
> ❌
Avoid using \* unless the webhook is fully public and returns no sensitive data.
{% endhint %}
## Reference table
| Header | Description | Example |
| ---------------------------- | ---------------------------------------- | ---------------------------------- |
| Access-Control-Allow-Origin | Defines which site may call your webhook | |
| Access-Control-Allow-Methods | Lists allowed HTTP verbs | GET, POST, OPTIONS |
| Access-Control-Allow-Headers | Lists allowed custom headers | Content-Type |
| OPTIONS | Preflight permission check | Must return 200 with headers |
## Handle OPTIONS preflight requests
Browsers send an *OPTIONS* request before certain POST or PUT requests to confirm that CORS is allowed. Your webhook must allow OPTIONS requests for this to succeed.
Add OPTIONS under the **Allowed Methods** field of your **Trigger Parameters** menu in workflow settings**.**
## Troubleshoot the CORS webhook trigger
#### Trailing slash in origin
Try removing the slash from the end of your domain.
#### Missing OPTIONS handler
Add the OPTIONS method to the webhook.
---
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