Microsoft Graph API Contacts Subscription - Not Receiving Notification

Question

We are migrating over from Outlook API that is deprecated to Microsoft Graph API. We have a working flow where we are subscribed to a user's contacts changed/created/deleted events.

I created a subscription and got back a 201 response and the following:

{"@odata.context":"https://graph.microsoft.com/beta/$metadata#subscriptions/$entity",
"id":"xxxxxxx",
"resource":"me/contactFolders/YYYYYYYYYYY/contacts",
"applicationId":"ZZZZZZZZZZZZ",
"changeType":"created,updated,deleted",
"clientState":null,
"notificationUrl":"https://xxxxxxx.com/xxxxxxx",
"notificationQueryOptions":null,
"notificationContentType":"application/json",
"lifecycleNotificationUrl":null,
"expirationDateTime":"2022-05-21T17:05:09Z",
"creatorId":"444444444444",
"includeResourceData":null,
"latestSupportedTlsVersion":"v1_2",
"encryptionCertificate":null,
"encryptionCertificateId":null,
"notificationUrlAppId":null}

However, I've tried to subscribe to just "me/contacts" instead of a specific folder as well but no matter what I do, my notification URL does not receive any notifications. I have subscriptions for email messages and that one works fine. Is there something that is different with receiving notifications from the old Outlook API vs Microsoft Graph's subscription notification?