To set up a webhook for notifications when a file is updated in OneDrive (business) or SharePoint, you need to ensure that you have correctly registered the subscription and that your application is set up to handle incoming notifications. Here are some steps and considerations to help troubleshoot why your API is not receiving notifications:

1.Subscription Registration: Make sure that your subscription is correctly registered for the specific resource you want to monitor (e.g., a drive or a list). The you provide must be publicly accessible and must support HTTPS.

2.Authorization: Verify that the user has authorized your app to access the OneDrive or SharePoint content. If the app does not have the necessary permissions, it will not receive notifications.

3.Testing: You can test the webhook by manually updating a file or list item to see if your endpoint receives the notification.