Hey there @reniel89! Emily here from Support Engineering 
To set up a webhook that triggers when an admin replies to a user in Intercom, you'll need to follow these steps:
- Go to the Webhooks page in your Intercom Developer Hub.
- Select the 'conversation.admin.replied' topic from the Webhook topics dropdown to receive notifications when an admin replies to a conversation.
- Ensure you have the correct permissions set on your Authentication page, as required by the webhook topic.
- Click Save to start receiving notification requests for the topics you've subscribed to.
This will allow you to receive real-time notifications of events happening in Intercom, specifically when an admin replies to a user message 
Here is the documentation on webhooks for further guidance: Webhooks Documentation 
Hope this helps! 