docs(tem): webhook notr (#3731)

Author: ldecarvalho-doc

managed-services/transactional-email/how-to/create-webhooks.mdx

@@ -31,6 +31,10 @@ You can set up webhooks for Scaleway Transactional Email and subscribe them to [
 
 ## How to create a webhook
 
+<Message type="note">
+You can create only one webhook per domain.
+</Message>
+
 1. Click **Transactional Email** in the **Managed Services** section of the [console](https://console.scaleway.com/) side menu. Your domains display.
 2. Click the domain for which you want to create a webhook.
 3. Click the **Webhooks** tab.