Webhooks allow you to subscribe to events in your HubSpot account, such as every time a contact is created or every time a specific property in a contact is changed. Rather than making an API call to query for event changes in your HubSpot account, you can subscribe to events which will trigger HubSpot to send an API request to an endpoint that you configure in your private app.

Webhook subscriptions were previously only available to public apps. This meant that if you wanted to enable webhooks, you'd have to create a separate developer account and a public app for that functionality -- even if you only wanted webhooks for your own portal.  Bringing webhooks to private apps makes them more accessible and easier to use within your existing account.

To start using webhooks in a private app, create a new private app or edit an existing one.

Your private app will have a new tab called Webhooks where you'll be able to set up the feature. Here, you can add a Target URL that HubSpot will make POST requests to when events trigger.

Click on Create subscription to select which events you'd like to create webhook subscriptions for.

You can now view, activate, pause, or delete your subscriptions. Once done, click on Create app or Commit changes to save your private app.

Now when your events are triggered, such as when a contact is created, HubSpot will send data to your target URL. You can view your webhook logs within your private app.

For more information, please refer to the documentation