Microsoft Graph API: Outlook Contact NOT Permanently Deleted with PermanentDelete.PostAsync()

I'm encountering an issue when attempting to permanently delete an Outlook contact using the Microsoft Graph API. The contact was previously inserted without any problems via the API, and I also assigned a profile picture to it, uploaded via the API.

Contact? contactAdded = await _graphClient.Users["{user-id}"] .ContactFolders["{folder-id}"] .Contacts.PostAsync(contactToBeAdd, cancellationToken: cancelToken);

I'm using the PermanentDelete endpoint as described in the Microsoft Graph documentation: https://learn.microsoft.com/en-us/graph/api/contact-permanentdelete?view=graph-rest-1.0&tabs=http My C# code looks like this:

await graphClient.Users["{user-id}"].ContactFolders["{folder-id}"].Contacts["{contact-id}"].PermanentDelete.PostAsync();

The code executes successfully without throwing any exceptions. However, when I check the Outlook application (desktop or web), the contact still exists. It appears that almost all of the contact's information has been deleted, but the contact itself remains visible and still appears in searches.

Has anyone else experienced this issue and can suggest a solution or an alternative approach to permanently delete Outlook contacts using the Graph API?

Thanks in advance for any help.